This is my 100th post! So to celebrate, here is a roughly chronological list of all the supporting characters in Barry Allen's life from the inception of the New 52 through the Trinity War. Everybody on this list has helped the Flash out at least once, but some of them have turned against him or regularly count themselves as rogues of the Flash. Hence the "Friends and Foes" titles.
Pandora
Pandora was the guiding force that helped the Flash turn the Flashpoint world into the New 52 world, although it is likely that she has forgotten that event along with everybody else. Pandora mysteriously showed up in the background shortly after Flash had his first encounter with Mob Rule. But Flash didn't officially meet Pandora until the Trinity War, when she was trying to find someone with a pure heart to open her box and remove the seven deadly sins from humanity. But it turned out that the box was actually a portal to Earth 3, which unleashed the Crime Syndicate on the world.
Nora Allen
Barry's mom was a guiding influence in his life, and he often repeats her words of encouragement and advice to keep moving forward. She once took him on a safari and fought off a crazed gorilla (Solovar) by throwing her camera at his face. Later, as she seemed headed toward a divorce, she was mysteriously murdered. This event motivated Barry to become a police scientist, and every year on the anniversary of her death, he reopens the case to try to find the true killer.
Henry Allen
Barry's dad didn't seem to play as large a role in his life as his mom did, but he did take Barry to the Bonneville Salt Flats in Utah several times to watch the cars race during Speed Week. Barry was impressed by the Salt Flats and goes there frequently as the Flash to run and clear his head. When Barry was 11, Henry was charged with murdering his wife, Nora, and sentenced to life in Iron Heights Prison. Barry refused to believe his dad was guilty, and he spent much of his life trying to prove his innocence. One year, Henry told Barry that he was guilty and that Barry should give up on him. Shortly thereafter, Barry became the Flash and realized that he no longer needs his dad to be innocent, but he wants him to be and will continue looking for it.
Solovar
Solovar was one of the first gorillas to come in contact with the Speed Force. He helped found Gorilla City, but he decided to travel to the future when he saw a vision of the end of the world. Unfortunately, he arrived too early, and found Barry when he was a little boy on a safari with his mom. Perhaps the time travel gave him temporary insanity, because he immediately devoured a gazelle and attacked Barry's van. But Solovar was hit with a tranquilizer dart, taken to a zoo, and calmly waited until Patty Spivot and Turbine visited him during Grodd's invasion. Solovar gave Patty a message to remind Barry that the mind is always faster, then he sacrificed himself to save the Flash's life. Solovar survived Grodd's attack, and he was rescued by his fellow gorillas.
Darryl Frye
Darryl was a friend of Nora's and became Barry's guardian after she was killed. A lifetime policeman, Darryl was eventually promoted to captain and was put in charge of Barry's division. But Darryl doesn't just stay behind a desk all day — during Gorilla Grodd's invasion, he personally led a squad out to battle the apes and rescue the human hostages. There is some speculation that Darryl is Barry's real father, but there has not yet been any confirmation made in support of or against that theory.
Manuel Lago
Manuel was one of Barry's best friends in college. He helped the shy kid come out of his shell and taught him the value of having a girl worth taking a beating for. Later, Manuel's parents were divorced, and Manuel's dad was killed soon after by the terrorist group Basilisk. Manuel not only blamed his mom for this, but he joined the CIA with the intention to avenge his father's death. Manuel got in a little deeper than he expected, though, and at one point lost his right hand and asked Barry to take him home. But the CIA wouldn't let him leave, and they subjected Manuel to an experimental treatment that enabled him to regrow his hand and turn into a super soldier of sorts. Manuel then defected from the CIA and began hunting down Basilisk by himself. He was eventually captured, and tortured by having his limbs repeatedly cut off. But Manuel's fallen limbs grew into clones of himself, and they helped him escape and continue his war against Basilisk. But when clones started dying off, Manuel tried to run away from the problem. The clones then tracked him down, and convinced him and Dr. Darwin Elias to fix their condition. But Elias' experiment failed, killing all his clones, and Manuel blamed him and the Flash. He then ran away to an unknown location and began rebuilding Mob Rule. He hasn't been seen since.
Malaya Lago
Malaya is the mother of Manuel, and she maintains a close relationship with Barry. She visited him after he was struck by lightning, and she opened up her home to Barry after he was nearly killed by Grodd.
David Singh
David was Barry's director at the crime lab until Barry got transferred down to the cold case room. David has a short temper, but is a good police officer and a good man. He never hesitates to help out on the streets, like during the blackout, and he offered comfort to Patty Spivot when she believed Barry was dead. David was also in a secret relationship with Hartley Rathaway, the Pied Piper, and he was quite upset when his boyfriend resumed his vigilantism. But when Hartley was seriously injured by the Weather Wizard, David immediately rushed to his aid, no longer concerned with who saw them together.
Harvey Bullcok
A few weeks after Barry graduated, he volunteered to help out in Gotham City during a massive blackout. Harvey was one of Barry's partners and helped him investigate a new drug called Icarus. Harvey saved Barry's life during their little adventure, and he taught him that the law isn't always completely black and white.
Spencer Thompson
Spencer was Barry's other partner during his brief stay in Gotham, but he very quickly went from friend to foe, as it was discovered that Spencer was involved in the Icarus drug. To cover his tracks, he attempted to kill Barry, but was gunned down by Harvey Bullock. But Harvey didn't report Spencer's wrongdoings because he knew Spencer was acting out of desperation for his sick daughter.
Iris West
Iris' mother died giving birth to her little brother, Daniel, and the two of them were raised by their abusive father. One night, Daniel pushed their dad down the stairs, accidentally paralyzing him. Daniel ran away, leaving Iris to care for her father by herself. But she managed to succeed in life, going to college and landing an internship with the Gotham Gazette. She first met Barry while in Gotham, and she helped him investigate the Icarus drug. She also helped save his life when he was nearly killed by said drug. The two soon began dating each other, but when Daniel was arrested for robbing a bank, he asked Iris to get her police boyfriend to reduce his sentence. When Barry caught wind of this, he felt Iris was using him, and he broke up with her. But they managed to keep a fairly close relationship, as Iris frequently used Barry as a source for her stories at the Central City Citizen. A few years later, she even tried to ask him out again, but by then he had moved on and was going out with Patty Spivot.
After the massive blackout in the Gem Cities, Captain Cold attacked the Flash. During that fight, Iris was sucked into the Speed Force along with three other people. The Flash eventually saved them, and they all acquired powers from the Speed Force. Although Iris' super speed wasn't manifest until she learned Daniel was the Reverse-Flash and had killed three people. Iris raced out to the Flash's fight with Daniel and Dr. Elias, and she was shot by Elias' gun that drained her of her powers. Daniel is now locked away in Iron Heights, and Iris is probably still sadly in love with Barry.
James Forrest
James was one of Barry's co-workers at the police lab. Although he is a bit on the chubby and goofy side, he is a good cop and a kind man. He visited Barry after his lightning strike, and he was one of the few cops to continue to support the Flash when Dr. Elias had turned most the town against him. Forrest was briefly captured by the gorillas during Grodd's invasion, and he inadvertently helped Barry discover the Reverse-Flash's identity.
Patty Spivot
Patty is a blood analyst at the Central City police lab. It took Barry two years to work up the courage to ask her out, but when he finally did, they never looked back. Patty played a big role in the Mob Rule and blackout saga, and survived a brief scare when it looked like Mob Rule had killed Barry. She assumed Barry was killed a second time, when a rift to the Speed Force sucked up four people. To take her mind of things, she decided to journey to Guatemala to investigate a cold case. She was promptly kidnapped by the Mardon family, and was rescued by the Flash. However, Patty blamed the speedster for her boyfriend's death, so Barry kept his distance from her for a while. But during Gorilla Grodd's invasion, Patty met Turbine and Solovar, and learned that Barry was the Flash. She helped rescue him from the rampaging gorilla. Patty then went out on the streets to help battle the gorillas, and she saved Captain Frye by shooting one of the apes. Patty also forgave Barry, accepted his superhero alter ego, and let him move into her apartment. Patty later helped discover the true identity, and she introduced Barry to her parents during their 30th anniversary.
Hal Jordan
Barry first met Hal when the two of them were investigating a case of missing children across the nation. The two new heroes discovered the kids were being abducted by aliens for gladiator-style games. Flash and Green Lantern traveled across the universe and saved the kids. Later, Hal called Barry when he and Batman were being attacked by Superman. Flash quickly showed up, battled the Man of Steel for a little, but then the heroes all realized they were on the same side, and worked together to battle the parademons and Darkseid. Hal was a founding member of the Justice League, and stayed with the team for five years. But he left the team after David Graves played a video of Hal fighting Wonder Woman across the world. Hal then became very busy with his Green Lantern responsibilities, but he did meet up with Barry again to bring the alien abductors from their first case to justice. Barry had to use Hal's ring during the fight, and the two friends gained a deeper appreciation for each other.
Captain Cold
Leonard Snart was one of the Flash's earliest and most persistent foes. Using his ice guns, Cold formed the Rogues with a strict code of conduct. But after repeated defeats at the hand of the Flash, Cold became desperate, and accepted an offer from Dr. Elias to receive super powers. The experiment did succeed in the strictest sense, but it caused more problems than it solved, and the Rogues turned against Cold. His sister, Lisa, became the leader of the team as the Glider, and she attempted to kill her brother. Captain Cold briefly teamed up with the Flash, but only really to fight his way back on to the Rogues. But then Gorilla Grodd invaded Central City, so Captain Cold and the rest of the Rogues struck up a quick, temporary alliance with the Flash. As soon as the gorillas were defeated, Cold and the Rogues retreated to the Mirror World.
Weather Wizard
Marco Mardon is a member of the Rogues. After he gained superpowers, he moved back to his native Guatemala to run the family mob with his sister-in-law. But when he found out she killed his brother, Marco killed her and returned to the Rogues. Marco then briefly teamed up with the Flash to help take down Gorilla Grodd and his army.
Heatwave
Mick Rory is a member of the Rogues who became especially mad at Captain Cold for giving them all superpowers. Mick has a hard time controlling his temper, and accidentally causes fires nearly everywhere he goes. He was especially eager to join Glider and attempt to kill Cold. He did reluctantly set aside his vendetta, and also helped battle the gorilla invasion.
Mirror Master
Sam Scudder is a member of the Rogues. His girlfriend, Lisa Snart, is Captain Cold's sister. When the Rogues all gained superpowers, Sam became trapped in the Mirror World, but he continues to be a tremendous asset to the Rogues. During the gorilla invasion, he helped rescue many civilians.
Pied Piper
Hartley Rathaway used to be a member of the Rogues, but he left them at some point to live a clean life. He became conductor of the Central City Symphony and started going out with David Singh. When the Flash disappeared into the Speed Force, Hartley returned as the Pied Piper, but this time as a hero. He tried to help Flash battle the Rogues, but he was quickly taken down by Weather Wizard.
Superman
Flash first met Superman during the Darkseid invasion. Superman initially attacked Green Lantern and Batman, and Flash helped pull him off them. The heroes soon teamed up and later formed the Justice League, having many adventures over a five-year span. Flash also helped Superman battle H'el and save the entire solar system in the process. The Trinity War was primarily caused by Superman's inadvertent killing of Dr. Light. It was later revealed this was caused by Atomica, who placed a small piece of kryptonite in Superman's brain.
Batman
Flash was surprised to discover Batman was a real person during the Darkseid invasion, and he was even more surprised to learn the Dark Knight does not have any superpowers. Batman was a founding member of the Justice League, and he also helped out in the battle with H'el. During the Trinity War, Flash primarily stayed with Batman in his quest to discover whether Dr. Light triggered Superman's heat vision.
Wonder Woman
Wonder Woman was a founding member of the Justice League, and is currently dating Superman. She reluctantly agreed to allow the League to help her track down Cheetah, and Flash had his calf muscle sliced open by the super villain. Wonder Woman also joined the Flash to fight H'el. During the Trinity War, Wonder Woman turned to her magic roots and enlisted the aid of Justice League Dark to try to save Superman.
Aquaman
Aquaman was a founding member of the Justice League, and he remained loyal to the team, even though he frequently felt he should have been the leader. The Flash was busy fighting Gorilla Grodd when Atlantis attacked the surface world, so Flash was unable to help Aquaman during his greatest crisis. Aquaman was present during the Trinity War, but stayed mostly in the background.
Cyborg
Vic Stone was nearly killed by parademons during Darkseid's invasion, but his dad saved him by giving him a robotic body, turning him into the hero Cyborg. He was able to acquire boom tube technology, which turned out to be key in repelling Darkseid. Cyborg helped form the Justice League, and Flash has kind of taken him under his wing, and has cheered him up from time to time. Cyborg helped battle H'el, and was heavily involved in the Trinity War. Although Atomica hacked into his systems, and his robotic part separated itself from him to become Grid.
Steve Trevor
Steve was Wonder Woman's boyfriend, which put him in perfect position to be A.R.G.U.S.'s liaison to the Justice League. But things got awkward when Wonder Woman dumped him. After he was kidnapped by David Graves, Amanda Waller replaced him. But Steve did become the leader of the Justice League of America, and got caught up in the Trinity War.
Martian Manhunter
J'onn J'onzz was briefly the eighth member of the Justice League, but for some reason things ended badly with a big fight. Martian Manhunter later joined the Justice League of America, recruited specifically to take down Superman. But during the Trinity War, he came to Superman's aid and tried to find out who caused Superman to kill Dr. Light.
Gloria White
One day, the Flash saved Gloria from an apartment fire, but he was too late to save her mom, who died of smoke inhalation. Gloria's dad, Dalton, always blamed the Flash for his wife's death, and two years later, he enacted a plan to teach the Flash a lesson. He planted two bombs in the building, and he injected himself with poison. Gloria, however, used the tragedy of her mom's death to become a paramedic, and she was on the scene when her dad had his meltdown. She was able to provide the Flash with some drugs that he sped up to save Dalton's life.
Captain Atom
The Flash met Captain Atom while he was helping out some rebels in Libya. Flash was initially worried about Captain Atom, but he quickly saw he was a good hero. The two formed a good pair, as Captain Atom was able to keep up with the Flash's super speed. But Captain Atom proved he could do much more than that when he absorbed the energy of a nuclear blast.
Darwin Elias
Dr. Elias is Central City's most prominent scientist, but his motives haven't always been necessarily pure. When he saw Captain Cold down on his luck, he offered to give the Rogues super powers "just to see what happened." Elias later became a great ally for the Flash. He helped the speedster learn about the nature of his powers, and he encouraged him to learn to think at super speed. Elias theorized that when Flash ran too fast he was causing temporal rifts, and he even suggested that they destroy the Speed Force. As a compromise, he gave the Flash a device that warned him when he went too fast. But a temporal rift opened up anyway, sucking four people into the Speed Force. When Flash tried to save them, Elias became embittered toward him and began to turn the Gem Cities against the Flash. He built a monorail using excess Speed Force energy collected from the Flash, and took all the credit for it. At the unveiling of the monorail, he was attacked by Glider, but she framed the Flash for it, which only increased Elias' hatred toward him.
Elias developed a gun to extract the Speed Force from the Flash, but he was soon attacked by the Reverse-Flash, who drained Elias' store of excess energy. The Flash arrived immediately after, and Elias chased after the two speedsters as they battled through the city. Ultimately, Reverse-Flash took Elias' gun from him and tried to use it on the Flash, but Iris intercepted the blast and lost her super speed. The Flash eventually defeated the Reverse-Flash and warned Elias to stay out of his way.
Green Arrow
Green Arrow tried to join the Justice League, and annoyingly followed them around for a few weeks. Eventually he was approached by Steve Trevor and became a founding member of the Justice League of America. Green Arrow also was involved in the Trinity War.
Floyd Gomez
Shortly after the blackout in Central City, Patty became interested in the Claudio Mardon murder case. Since Iris wrote a story on it, Patty dragged Barry out to meet her for lunch to try to get some more details. They met on a restaurant on a boat, while Gomez was there on a date with his girlfriend. Captain Cold soon attacked, and while the Flash battled him, a portal to the Speed Force opened up over the boat, sucking in Iris, Gomez, Marissa and Albert. After the Flash eventually saved them, Gomez gained super strength. He tried to become a superhero named Sprint, but his career was quickly shut down by the Flash. The Reverse-Flash then tried to kill Gomez. He evaded the first attack, warned Albert, and lived on the run for a while. But he couldn't avoid the Reverse-Flash forever, and was eventually killed.
Marissa Rennie
Marissa was sucked into the Speed Force with her boyfriend, and she initially lied about gaining powers. But she used her ability to make things blow up to commit some robberies. One robbery went poorly, and she accidentally killed a security guard. The Trickster was blamed for the murder, and when he was taken to Iron Heights, his friends the Outsiders tried to break him free. Albert decided to go over there to help, and since Gomez wasn't around, Marissa went with him. But instead of helping out, Marissa tried to kill the Trickster to protect her innocence. Albert and Barry stopped her, and Marissa was locked away. But she was killed by the Reverse-Flash while in prison.
Albert Lim
Albert was sucked into the Speed Force with Iris, Gomez and Marissa. When they were rescued, Albert found he had the power to boost up and improve any gadget he touched. He tried to be the superhero named Turbo Charger with Gomez. The two of them had a hard time tacking down the Trickster, and the Flash gave them a very stern lecture. Albert then helped quell the riot at Iron Heights caused by the Outsiders. He teamed up with Barry Allen (who had temporarily lost his powers to Dial H), and Albert turbocharged one of Captain Cold's guns to freeze Marissa before she could kill anybody. Later, Gomez warned Albert about the Reverse-Flash, so he built a high-tech security camera to protect himself. The camera didn't save him from the Reverse-Flash, but it did record his death, which Barry was able to watch and gather clues from about the Reverse-Flash's identity.
Turbine
Roscoe Hynes was a World War II-era pilot who was sucked into the Speed Force, where he stayed for 70 years. He was able to watch Barry Allen grow up, and he gained the ability to create whirlwinds. But spending too much time in isolation wasn't good for Turbine's sanity. Periodically, a window in the Speed Force would open up, and Turbine would try to escape through it. But all he could do was pull things in, including Iris, Gomez, Marissa and Albert one time. When Flash journeyed to the Speed Force to save them, he only met Turbine, and pulled him out. Turbine begged Flash to tack him back in time so he could be reunited with his family, but Flash refused to risk time travel. Turbine was disappointed, but he helped out during Grodd's invasion. He led Patty to Solovar, and soon teamed up with the Rogues to save civilians from the gorillas. Mirror Master then showed Turbine a vision of his family, and offered him a spot on the Rogues. Whether Turbine accepted and where he currently is remains to be seen.
Glider
Lisa Snart was not initially a member of the Rogues, but her brother s Captain Cold and her boyfriend is Mirror Master, so she's always hung out with them. She happened to be present when they gained superpowers, and she gained the ability to create an astral projection of herself. Once she mastered her new powers, she reunited the Rogues, tried to kill her brother, attacked Dr. Elias, and stole his monorail. Captain Cold fought his way back onto the team, but then Gorilla Grodd invaded the city, so Glider and the Rogues struck a brief alliance with the Flash. Once the gorillas were gone, Glider escaped into the Mirror World with the rest of the Rogues.
Simon Baz
When the president heard a suspected terrorist acquired a Green Lantern ring, he called in the Justice League. Flash and the others met Simon Baz and tried to help him out, but he ran away from them to try to find the real bomber who framed him. Simon was later recruited by the Justice League of America to take down Hal Jordan. During the Trinity War, Simon ended up on Batman's team with the Flash, and he saved Cyborg after his robotic part separated from him.
Guy Gardner
Guy is one of the Green Lanterns, who has somewhat of a bad reputation. When Flash heard one of the Green Lanterns could dead, he joked that he hoped it was Guy. But when the Rise of the Third Army events required to Guy to put his family in protection, Flash was happy to help them at the Justice League Watchtower, and he even gave them Thai food.
Charles the bartender
When it appeared that Barry Allen had been sucked into the Speed Force with four others, he needed to find a new job. So he went to the Keystone Saloon, a popular hangout for the Rogues. Charles was initially hesitant to hire "Al," but he gave him the job when Al created a drink that wouldn't freeze instantly in Captain Cold's grasp. Charles was a very laid-back boss, allowing Al unusually long bathroom breaks. After Barry Allen was "rescued" from the Speed Force, he had to wait for the paperwork to clear before he could work for the police again. Luckily, he still had his job at the bar, and was able to keep track of the Rogues there. Barry's now back with the police, but Charles is still running the saloon, catering to all criminals who frequent it, and yelling at them whenever they break a TV or something.
Superboy
Flash first met Superboy when Superman called in the Justice League to help him fight H'el. Familiar with Kid Flash of the Teen Titans, Superboy thought Flash's name was Man Flash. The heroes were eventually able to defeat H'el, and Superboy went on to have his own adventures.
Shay Veritas
Dr. Veritas is an ally of Superman's, who has a lab near the center of the Earth. When Superman recruited the Justice League for the fight against H'el, he took them to Veritas' lab first to gather information and form a strategy. Veritas provided some help from a distance, but Flash hasn't dealt with her since then.
Supergirl
The Flash's job during the H'el fight was to find Supergirl and convince her to leave H'el. Supergirl refused to listen to the Flash, though, and they got into a pretty big fight. Flash resorted to grabbing a weapon from Superman's trophy room, but H'el teleported him away before he could use it. Supergirl later realized H'el was evil, and she risked her own life by shoving a piece of kryptonite in his chest.
Firestorm
When Atlantis invaded the surface world, Cyborg was forced to call in several other heroes to help. The Justice League then decided it was time to expand their ranks, so Flash suggested they invite all potential candidates to the Watchtower. During their meeting, Platinum went berserk, and Firestorm was one of the heroes that stopped her. He then became a member of the Justice League, and was involved in the Trinity War. Amanda Waller asked him to learn to create kryptonite in case Superman needed to be stopped. While Firestorm didn't have to take down Superman, his new skill did help him locate the piece of kryptonite placed in Superman's brain by Atomica.
Black Canary
Black Canary accepted the Justice League's invitation to visit the Watchtower, but for whatever reason, she did not join the team.
Zatanna
Zatanna was invited to the Watchtower, but declined joining the justice League, saying she still wanted to solve her father's murder. But she did offer to help whenever she was needed, and she was needed when Shazam sparked an international incident by visiting Kahndaq. Since Shazam's powers are magically based, Superman invited Zatanna to provide some magic support in the Trinity War.
Black Lightning
Black Lightning was invited to the Justice League Watchtower with his friend, Blue Devil, but he declined the League's invitation, saying he wanted to keep his work on the small scale with schools.
Blue Devil
Blue Devil initially thought the Justice League didn't want him, and he tried to assure them he was in control of his demon suit. Batman told him that wasn't an issue, but once Black Lightning backed out, Blue Devil followed.
Element Woman
Element Woman was invited to the Watchtower, and she was one of the heroes who helped stop the rampaging Platinum. She then became a member of the Justice League, and was involved in the Trinity War.
Goldrush
Goldrush was invited to the Watchtower, but she made the Flash feel uncomfortable with her flirting. He referred to her as "Golddigger" and voted for her to not be on the Justice League. Goldrush was also taken down by Platinum very quickly, proving that she probably wouldn't have lasted long as a Leaguer anyway.
Nightwing
Batman's former sidekick only went to the Watchtower because he thought there was an emergency. He immediately turned down the Justice League's offer without discussion.
Platinum
Platinum was a robot created by Dr. Will Magnus. During the big meet-and-greet on the Watchtower, she went berserk and began attacking everybody. She was eventually shut down by Element Woman, Firestorm and Atom, but the whole event was actually a big diversion to allow Atomica to steal the Justice League's files from their entire five-year history.
Vixen
Vixen was invited to the Watchtower, but she was taken down by Platinum and did not become a member of the Justice League.
Atom
Rhonda Pineda was a student at Ivy University, and an unsung hero during the Atlantis invasion. Cyborg tracked her down and invited her to the Watchtower, but she didn't show herself until just after Platinum was defeated. Atom was named a member of the Justice League, but she was secretly spying on them for the Justice League of America. But during the Trinity War, she revealed herself to actually be Atomica from Earth-3. She came to this planet with the Outsider, and began a long, elaborate plan to bring the rest of the Crime Syndicate here. She placed a piece of kryptonite in Superman's brain, causing him to use his heat vision on Dr. Light and kill him. Atomica also hacked into Cyborg's system, and discovered his robotic side had become sentient and referred to itself as Grid. Atomica's boyfriend is Johnny Quick, the alternate Flash on Earth-3.
Frankenstein
One day, while passing through New York, the Flash saw a bunch of monsters attacking the city. He soon came across Frankenstein, who he mistakingly thought was another monster. Flash soon began working with him and the rest of the Justice League Dark. They discovered that the monsters were being created by Dr. Destiny. Flash helped them defeat him, and later ran into them during the Trinity War.
Madame Xanadu
When Flash met Frankenstein, he suggested they first find Madame Xanadu. So Flash ran and grabbed her, saving her from nightmares of her long lost lovers. While fighting Dr. Destiny, Xanadu admitted that the villain is her son, and she shocked everyone by killing him. Emotionally distraught by this, she briefly left the Justice League Dark, but was soon kidnapped by Plastique so she wouldn't warn the others about the Trinity War.
Deadman
Deadman is a member of Justice League Dark, but he was also recruited by Steve Trevor to join the Justice League of America. Flash first met him during the Dr. Destiny fight, and they were reunited during the Trinity War. They both ended up on Batman's team, and Deadman journeyed to heaven with Batman, the Phantom Stranger and Katana to find Dr. Light.
John Constantine
Flash met Constantine during the Dr. Destiny fight. He had alienated the members of Justice League Dark, but Flash convinced them all to give Constantine another chance and work together. Constantine also played a major role in the Trinity War, as he was the only one to be able to handle Pandora's box without becoming corrupted. But he couldn't prevent the Outsider from opening the box and bringing the Crime Syndicate to this world.
Swamp Thing
When the House of Mystery was stolen from Constantine, he summoned Swamp Thing to help him find it. But Dr. Destiny captured Swamp Thing and began exploiting his power. Flash and Justice League Dark saved Swamp Thing, and together, they all defeated Dr. Destiny.
Kid Flash
During the Reverse-Flash mystery, Flash saw a quick glimpse of the murderer on Albert's security camera. Remembering that Kid Flash also wears a lightning bolt symbol, Flash decided to track down the Teen Titan to see if he was involved in the case in any way. But Flash kind of spooked the kid, and he ended up chasing him around the world before he could finally talk. Flash realized that Kid Flash doesn't derive his powers from the Speed Force, which meant that he wasn't a potential victim of the Reverse-Flash. So Kid Flash returned to the Teen Titans, and Flash promised to meet up with him again later.
Shazam
After the death of Black Adam, Shazam felt it was only fitting to spread his ashes in his home of Kahndaq. But the country is a war zone and off limits to Americans, so the Justice League and Justice League of America scrambled to pull Shazam out of there before anything bad happened. What did happen, though, was the Trinity War. At one point, Shazam seized Pandora's box, which sent a shockwave to magical users throughout the world. But in the end, the Outsider won, and used the box to bring the Crime Syndicate to Earth.
Catwoman
Catwoman was brought into the Justice League of America to take down Batman, but she teamed up with him and the Flash during the Trinity War. Perhaps her biggest contribution during the event was figuring out how to open the House of Mystery by asking nicely.
Dr. Light
Arthur Light was recruited by the Justice League of America to take down Firestorm. He didn't like the idea of fighting a couple of kids, but he was hoping ARGUS could help him control his powers. Plus, Amanda Waller was kind of threatening his family. When the JLA met the Justice League in Kahndaq, Dr. Light stepped forward to try to get everybody to calm down before they started fighting. But when he got too close to Superman, his powers went berserk. Atomica then planted a piece of kryptonite in Superman's brain, which activated his heat vision and killed Dr. Light. Batman was convinced Dr. Light intentionally caused Superman's heat vision, and he journeyed to heaven with the Phantom Stranger to interrogate him. Unfortunately, Dr. Light had no memories of his death, and was required to stay in heaven.
Vibe
Cisco Ramon was recruited by the Justice League of America to take down the Flash. And although he was quite worried at first, one he turned his vibrational powers on the Flash, he actually caused some damage. But later, Vibe joined the Flash as a part of Batman's team.
Hawkman
Hawkman was recruited by the Justice League of America to take down Aquaman, who he did battle during the initial skirmish. But as with the other JLA members, Hawkman eventually joined with his intended target, and spent most of the Trinity War in the background with Aquaman.
Katana
Katana was recruited by the Justice League of America to take down Wonder Woman. She later joined Batman's team and journeyed to heaven with him and the Phantom Stranger to find Dr. Light.
Stargirl
Stargirl was recruited by the Justice League of America to take down Cyborg. She was present during the Trinity War, but was mostly just in the background.
Amanda Waller
Amanda Waller is the head of A.R.G.U.S. and the brains behind the Justice League of America. Although she used blackmail and underhanded techniques to recruit that team, she does have good intentions. Many heroes suspected her of causing Trinity War, but she didn't, and tried to work with them to solve the crisis.
Phantom Stranger
The Phantom Stranger is one of the Trinity of Sin with Pandora and the Question. Seeking to redeem himself, he became involved in the Trinity War and took Batman, Deadman and Katana to heaven to interrogate Dr. Light. Light didn't have any information for them, so Phantom Stranger tried to take him back to the world of the living to at least clear Superman's name. But this was a big no-no for Phantom Stranger, and he was punished by the angel Zauriel.
Black Orchid
Black Orchid is a member of Justice League Dark, although she was not present during the fight with Dr. Destiny. She was involved with the Trinity War, but mostly just in the background.
The Question
The Question is one of the Trinity of Sin, and he tried to help find who framed Superman for murder. His initial investigation led them to Dr. Psycho, but that turned out to be a dead end. Ultimately, the Question ended up fighting for Pandora's box just like everybody else.
Next time: Even though the recently-released Flash #27 clearly happens before Forever Evil, I'm going to proceed with my Forever Evil coverage, beginning with The Flash #23.3/The Rogues #1. Brian Buccellato's final run on The Flash will have to wait till I'm done with this epic event.
