Two weeks after his birth, Jefferson's father was killed in an IED explosion while serving in Somalia, hurting both him and his mother. He also watched many horror movies with his mother.
As a senior in high school, Jefferson was a promising football quarterback and a 4.0 student. On December 11, 2013, Jax led his school to a victory at the state championships while scouts from colleges watched from the stands. These scouts were instantly impressed by his performance on the field, and his coach told him that he was talented enough to go to any school he wished. Shortly afterward, the S.T.A.R. Labs particle accelerator exploded, creating a huge wave of dark matter that spread over the city. Upon seeing the wave of energy approaching, the attendants of the game ran for their lives, causing a stampede that held up one of Jax's injured teammates who relied on crutches to get around. Jax aided his teammate to safety inside of the high school, but before he could close the doors, he was struck by the dark matter at such a high speed that he was thrown backward into a wall, knocking him unconscious and slamming him into the floor.
Jax woke up in the hospital and quickly learned he could never play football again because of a permanent injury to his knee caused by explosion. Because his family couldn't afford college and his only hope of attending college was with a football scholarship, he was ultimately forced to find a full-time job as a mechanic to support himself.
Two years later, Jax was approached by Barry Allen and Professor Martin Stein at the auto shop where he worked. Barry and Stein had sought him out because the dark matter wave from the particle accelerator explosion changed his body's molecular structure in a way that made him one of two perfect matches to Stein, who, due to the death of his literal other half, Ronnie Raymond, was dying as a result of his powers becoming unstable from a lack of merging and needed to find a new partner. When he went to S.T.A.R. Labs to learn more about it and met Barry Allen's team, he refused to merge with Professor Stein and become a superhero, a decision that caused him to be berated by Caitlin Snow, Ronnie's widow, for his supposed inability to take responsibility, as she did not know about his family's financial situation and had assumed that he blew off college out of laziness despite his perfect grades. Caitlin later showed up at his auto shop and apologized for her behavior, explaining that her missing husband, Ronnie Raymond, became a hero as Firestorm and saved the city from the singularity, inspiring Jax. They are attacked by Dr. Henry Hewitt (The other candidate to become the new Firestorm) and escape to S.T.A.R. Labs, where Jax agrees to merge with Stein to save him resulting in the two becoming the new Firestorm. When Hewitt is wreaking havoc on Jax's old football field, he teams up with the Flash to stop Hewitt and starts to get used to his new superhuman abilities. Afterwards, he and Professor Stein go to Pittsburgh to train on Firestorm's abilities similar to Ronnie.
Aiding Rip Hunter
In January 2016, Jax and Martin Stein are still in Pittsburgh, where they are up against a criminal at a chemical plant as Firestorm. Stein tells Jax to be careful, as 83% of the chemicals are flammable, however Jax still shoots fireballs all over the place. While Firestorm does defeat the man, Stein is still upset that Jax doesn't listen to him, Jax tells him to stop treating him like one of his "snot nosed undergrads" when they are intercepted by Rip Hunter. Jax and the rest of Rip Hunter’s recruits woke up on top of a building where Rip informed them of the impending threat of Vandal Savage’s conquest of the world and a chance to join him. Later, Jax and Stein discussed Rip’s offer where Jax was firmly against it while Stein relished the opportunity. However, Stein drugged him and took him on Rip Hunter’s mission anyways.
Exploits in 1975
Jax woke up as the team is en route to St. Roch in 1975 and was angry with Stein. Jax was left behind in The Waverider when Chronos attacked. Jax merged with Stein and provided cover for the team to escape. After learning of Rip Hunter’s status as a rogue Time Master, Stein and Jax discussed leaving, but Jax had a change of heart because he likes being part of a team, reminding him of his days as a football star.
They tracked down Savage to Norway. However, Savage recognized that they weren’t terrorists and a huge fight broke out. Firestorm fought off Savage’s criminal allies, but Ray Palmer left a part of his A.T.O.M. Exosuit behind, altering history. Jax accompanied Stein and Sara as they meet with Stein’s younger self from 1975 in order to track down the lost part. They stole young Stein’s alpha-particle tracker and used it to take Ray’s tech back from Savage’s minions, but young Stein tracked them back to the Waverider. After the younger and elder Steins got into an argument, Jax consoled the elder about how arrogant both himself and his younger self are but also how selfless and intelligent he has become. After the younger Stein was escorted off the ship, the team was contacted by Snart, who had been captured by Savage. Firestorm took down Savage and the team escaped. While Carter Hall and Kendra Saunders went to finish him off with the Amon Dagger, the rest of the team held off Savage’s forces. However, Savage managed to get the upper hand and killed Carter and wounded Kendra forcing the team to retreat back to the Waverider. Aftterwards, Jax and the rest of the team reaffirmed their commitment to defeating Savage in memory of Carter.
While stuck in Leipzig in 1975, Jax was tasked with fixing the jumpship which was damaged during Chronos’s attack. Leonard and Mick were getting bored on the Waverider so they convince Jax to fly them to the Central City Museum to steal the Maximillian Emerald to give it to Leonard’s father. After Rip and Sara were captured trying to rescue Carter’s body, Jax flies the jumpship to rendezvous with the team at the Grayhill building. Later, Jax was present at the funeral they put on for Carter and Aldus.
1986 and the Cold War
The team’s next mission took them to 1986 to break into the Pentagon to steal a file on Savage’s current whereabouts. As Firestorm, he was tasked with creating a diversion by cutting the power, however he accidentally tripped the alarm, but they succeed on getting the file. The file directed them to the Soviet Union. After Time Master Druce set a trap for Rip, he is rescued by Jax, Stein, and Mick but Jax is wounded. Stein and Jax get into an argument where Jax is angry that he has to take all of shots, was unwillingly brought on the mission, and was forced to leave behind his life and his widowed mother in 2016.
On board the Waverider, Jax felt Stein’s fear as he was being held and tortured in Koshmar. Jax and Kendra use the link between him and Stein to send him a sign by cutting a message on his arm, which would then appear on Stein’s saying that they were coming. Frustrated with being left out of the rescue efforts, Jax and Kendra convince Rip to let them help. Kendra flies Jax into the prison and he cuts the power to the locks causing a prison riot. After Stein is unwillingly fused with Valentina Vostok to create Soviet Firestorm, Jax inspires Stein to break the merge. After Vostok began to destabilize, they retreated to the jump ship. Later he and Stein make amends and Stein expressed his gratitude to have Jax as his partner. After another attack by Chronos, the Waverider is hit and the team is stranded in 2046.
Detour from the mission
After the team arrived in Star City of 2046, they are attacked by the Green Arrow. They retreated to the ship where Jax diagnosed the repairs that are required to get the Waverider operational again. He wanted to have Kendra’s help in repairing the engines, and started to flirt with Kendra as they make repairs. Stein was able to deduce from his psychic link that Jax has a crush on Kendra and tries to deter Ray from getting close with Kendra. Stein's effort backfired, upsetting Jax but Stein told him to have more confidence in himself. Later, Sara Lance went off on her own to rescue the Connor Hawke, but the team came in to save Connor, Oliver, and Sara. Back on the Waverider, Jax overheard Kendra turning down Ray and had second thoughts about asking her out.
While in the Temporal zone, the Waverider received a distress call from the Acheron. Jax, Martin Stein, Rip Hunter, and Mick Rory investigated the ship but were captured by time pirates along with Captain Eve Baxter. After Mick went to make a deal with the pirates, Stein was able to sneak aboard the Acheron and free them. Jax, Stein, and Baxter acted as a distraction while Rip activated the airlock sucking the time pirates into the vacuum of space. In the aftermath of the battle, the team decided that Mick was too much of a liability, so Snart volunteered to put him down.
Foray into 1958
The updated timeline data from the Acheron pointed to Harmony Falls, Oregon in 1958 as the next place to find Savage. Jax was put in charge of gathering information from the local teenagers about a series of murders. After meeting Martin and Sara during their lunch hour in a diner, he talked to Betty Seaver but some jocks tried to intimidate him. Betty asked him out for tomorrow night. On the date, Jax asked Betty about her ex-boyfriend Tommy, who went missing. Before she could say anything, they were harassed by guys from the diner and then a horrific creature resembling Tommy attacked them. After fleeing the scene, they were pulled over by a police officer. Jax pleaded to the cop to get Betty medical help but was kidnapped by the cop. Jax woke up inside Savage’s Hall H wing and was given a dose of an Nth metal meteorite, mutating into a Manhawk. After Savage released him from his cell, Jax attacked Martin and Leonard but was knocked out by Sara. Stein and Gideon then synthesize a gene-therapy antidote curing the Manhawk mutation. He said goodbye to Betty and told her to someday get out of Harmony Falls. The Waverider was then attacked by Chronos again and the crew was forced to leave behind Kendra, Ray, and Sara in 1958.
In the aftermath of Chronos’ attack, Jax and Stein found Rip but discovered that Leonard was taken by Chronos. Due to the attack, the Waverider’s navigation was damaged so the ship touched down in 1960 instead of 1958. They picked up Kendra and Ray in Hub City. They then went to pick up Sara who had rejoined the League of Assassins, but due to temporal drift, she had become detached from her former self and captured them. After Sara and Kendra face a trail by combat, Sara refuses to kill Kendra but Chronos attacks the League. She convinced Ra's al Ghul to free the team and they all take down Chronos, only to discover that Chronos was actually Mick.
2147 and the rise of Savage
The team next traveled to the Kasnia Conglomerate in 2147 to stop Savage before his rise to power. Jax, Martin, and Ray gathered more information on the A.T.O.M. robot police force Kasnia uses to enforce order. After the rest of the team kidnapped Per Degaton, Jax suggested dropping him off in the Stone Age instead of killing him. In retaliation, Savage and Tor Degaton’s forces surrounded The Waverider. Jax, Sara, and Snart held off the soldiers and A.T.O.M. robots while Kendra and Ray disabled the robot command center, but Sara got captured by Savage. After failing to kill Per Degaton on his own, Rip then exchanged Per Degaton for Sara and the team retreated afterwards, but failed to stop Savage’s rise to power. Mick then informed the team of The Hunters who will now go after them since Chronos’ mission failed.
On the run from the Time Masters
Hiding from the Hunters, the team touched down in Salvation in 1871, a fragment in time invisible to the Time Masters. After Leonard shot a member of the Stillwater Gang for fighting with Martin, the team got into a bar fight before Jonah Hex settled things down. Hex then demanded to speak to Rip about dealing with Jeb Stillwater. Ray, Leonard, Mick, and Jax went to arrest Stillwater, but Jax was taken hostage. Rip challenged Stillwater in a quick draw to free Jax which Rip won, killing Stillwater. However the Time Hunters arrived and a huge fight broke out between the Hunters and Rip Hunter's team. The team defeated the Hunters and Jax excitedly proclaimed victory. However, one of the Hunters warned of The Pilgrim, who Mick confirmed will come after their younger selves.
In Central City of 1990, the team first went to save Mick Rory’s younger self. Mick tasks Jax with watching over young Mick. After targeting Sara Lance’s self from 2007, Firestorm saves Ray Palmer’s 2014 self from The Pilgrim but discovered her powers of temporal micro-manipulation. The team then switched tactics to abduct their selves as newborns. Jax revealed that he never got to see his father because he shipped off to Somalia before he was born. However, in Central City of 1993, Martin and Ray saw that his father had not shipped off to Somalia yet and retrieved Jax so that he could talk to his father. Then The Pilgrim showed up in 1993 to newborn Jax’s empty crib. The team took the younger versions of them all to The Refuge where they learned a little of Rip Hunter’s past. After returning to the Waverider, Jax was saddened that he didn’t tell his dad about his fate in Somalia and about what he missed out on without a father. The Pilgrim contacted the Waverider to say she had taken James Jackson and other loved ones and threatened to kill them unless they turned themselves in. Rip counters the Pilgrim’s offer by offering his younger self in exchange for the team’s loved ones and younger selves. When the exchange of James Jackson for young Rip Hunter was made, the team attacked The Pilgrim. She managed to hold them off with her time manipulation powers until young Rip stabbed her in the leg and the team subsequently destroyed her. Jax then had one last conversation with his father telling him to be careful for IEDs while on his army tour.
Taking the fight to Savage
Running out of time to kill Savage, the team traveled to the only time they knew for certain where he was, 2166. Jax accompanied Rip, Ray, and Martin to make contact with the resistance where he offered a candy bar to a refugee child. After capturing Cassandra Savage, the Waverider was attacked by the Leviathan. Martin was injured in the attack and asked Jax to take care of the refugees. Once the team came up with a plan to take out Savage, Jax assisted Ray in modifying his exosuit to grow in size to fight the Leviathan, and monitored Ray from the Waverider as Ray battled the giant robot.
The team analyzed the Leviathan and determined that the technology it uses is more advanced than anything in 2166 and that Vandal Savage must also have been manipulating time. Rip decided to take Savage to the Vanishing Point for punishment before the Time Masters Council for messing with time. However the ship’s time drive had taken too much damage and Rip tasked Jax with fixing it. However, temporal radiation leaked from the time drive, causing his body and organs to age at an accelerated rate, but he succeeded in restoring the time drive. Martin then put Jax onto the jump ship to 2016 and deduced according to his theory of quantum-retro causality that the trip back to 2016 should reverse the side effects of the temporal radiation.
Jax arrived back in 2016 cured of his temporal ailments and enlisted the help of Martin. They scavenged Eobard Thawne’s Time sphere for parts to the jump ship. After repairing it, he told Martin that his present-day self would be very angry for drugging him but that he was very thankful for Martin’s decision to bring Jax along. Jax then time traveled to the Vanishing Point and arrived just in time to save the team from Time Master Druce's soldiers. Firestorm held off the reinforcements while the team figured out how to self destruct the Oculus. Once Leonard sacrificed himself to destroy the Oculus, the team left the Vanishing Point.
Rip brought the team back to Star City of 2016 because Vandal Savage had been lost to history after taking Kendra and Carter/Scythian. After everyone tried going back to their separate lives, they met back in Star City at the spot where the Waverider dropped them off. The team then found a message from Kendra hidden in an old helmet in Rip’s quarters leading them to Saint-Lô, France in 1944. The team then attacked Savage and rescued Kendra and Carter, with Jax discovering a new power of transmutation. Jax and Stein then tried to replicate the power but with no success. The team later figured out Savage’s plan to undo time by detonating three Thanagarian meteors in three different time periods. Jax, Martin, and Sara went after Savage in 1975 while the others went after him in 1958 and 2021. After Sara killed Savage of 1975, Firestorm used transmutation to turn the meteor into water and prevented it from detonating. The team then rendezvoused in St. Roch of 2021 but the radiation buildup from the third meteor prevented Firestorm from transmuting it. Rip piloted the Waverider to fly into the sun with the meteor saying his goodbyes to the team. However, Rip angled the ship to eject the meteor and time jumped back 20 minutes and rejoined the team in St. Roch. He then offered the team to join him in protecting the timeline now that the Time Masters are gone. Jax and Clarissa have an intervention with Martin convincing him to go. They meet back in Star City where Kendra and Carter leave the team now that Savage is finally gone. Then, another damaged Waverider crash lands with a man named Rex Tyler from the Justice Society of America telling them not to board the Waverider.
Jax was a very hard worker academically and athletically. Knowing his parents couldn't afford college, he focused hard on school to get a 4.0 and was eventually rewarded with a football scholarship. He also cared about the well-being of other people. During the night of the particle accelerator explosion, he saw an injured person on the field and didn't even hesitate to help them to safety, which resulted in his knee being injured from the explosion. Following that, he entered a depression as all of his hard work had been for naught and he had to work as a mechanic for a living because he lost his only means to afford college.
Jax eventually becomes happy again when he found his calling to help people by becoming Firestorm. He also displays high amount of potential as Firestorm as Martin Stein quickly changed his opinion of him when he was chosen to be the next Firestorm. Given, his original opinion was when he knew nothing of Jax other than he was a high school graduate compared to a well accomplished scientist who was the other candidate. Since joining the team, Jax has developed a crush on Kendra Saunders, though it has seemed to pass.
Despite his good traits, he is arrogant and egotistical to the point of being immature, when these traits started to put the Legends mission to stop Vandal Savage in danger, Martin was then forced to tell him to grow up and not everything is about him. These traits seem to have disappeared after this, especially after Martin was captured by Vandal.
In battle, he is willing to put all of his power to use and not restrain them. He is shown to be willing to kill in battle, such as using a gun to fight in the Old West and he personally tried to deal a death blow on Chronos until he was revealed to be Mick Rory.
Due to his background and ethnicity, Jax has always expected to deal with racism and bigotry. However, when going undercover at during the American Civil War, and getting to experience the kind of cruelty of slavery towards black people firsthand, Martin felt a surge of hatred, anger, and fear well up inside of Jax that he had never felt before, so much that through their psychic link, the sheer weight of Jax's emotions stunned him physically. Jax discovered a sense of pride in his culture and his roots when he saw the indomitable spirit of the people enslaved along with him. Suffice it to say, he felt a profound sense of satisfaction in seeing the slave owner's plantation and mansion consumed in the inferno he had started.
After learning of the message sent by Barry Allen from the year 2056 and that he altered the timeline, he did not criticized the present Barry for his actions, as Jax he would do exactly the same thing the latter did, if he was in an emotional state, and not thinking clearly; as Jax is no hypocrite.