Jefferson “Jax” Jackson (born September 12, 1993) is a mechanic. After the death of Ronnie Raymond, he took his place as one half of the transmuted and conjoined meta-human called Firestorm alongside Martin Stein. Jax was then recruited by Rip Hunter on a mission to take down Vandal Savage; though Jax was initially unwilling to join the team, Stein, who was desperate to become a time traveler and knew that he couldn’t be separated from Jax for long without his powers becoming unstable, drugged him and forced him to come along. Despite joining the team against his will, Jax later grew to like being part of the team, and he began to act as the mechanic of the Waverider as well as a member and the second-in-command of the Legends, a group of people dedicated to protecting the timeline from time criminals.
After the death of Martin, Jax takes a leave of absence from the team with their blessing.
Five years after leaving the Legends, Jax is happily married and has a daughter, Martina Jackson, named after Martin. He briefly re-allied with the Legends in order to stop Mallus.