Bartholomew “Bart” Allen was born in the 31st Century to Meloni Allen. In his teen, Bart was hit by lightning which not only gave him amnesia but also sent him to the year 2004, with the ability to super speed.

The only thing that Bart could remember was three names: Jay Garrick, Barry Allen and Wally West. Setting himself up in Metropolis, Bart supported himself as a petty thief and acquired fake I.D.-cards, under the three names in his head.

In 2004, Bart saved the life of Jonathan Kent and stole the man's wallet. What Bart didn't realize was that he had been seen by Jonathan's son, Clark, who could also move at superhuman speed. Using Jonathan's credit card to pay for a hotel room, Bart was confronted by Clark, but decided to make a run for it and was chased through Metropolis by Clark. Amazed to see another person able to move like him, Bart headed to Smallville and tried to befriend Clark.

Wanting a better life, Bart stole a manuscript from Lex Luthor. Unfortunately for Bart, his fencer double crossed him and made a deal with Lex. However, after the fence and Lex got into an argument, Lex was knocked out and the fence decided to kill Bart. Bart was saved by Clark, but Bart immobilized him with Green Kryptonite and planned to take off. Clark pleaded with him to do the right thing, which prompted Bart to put away the Kryptonite. Afterwards, Bart chose to return the manuscript to Lex.

Dropping by the Kent Farm, Bart announced that he was going to travel the world and see if there was anyone else out there, like him and Clark. Clark tried to convince him to stay. Bart replied that he'd think about it if Clark could catch him. Bart and Clark raced out of Smallville, until Bart ran too fast for Clark to follow.

At some point over the next two years, Bart found himself in Star City and met Oliver Queen, who took him in. Bart later became one of the members of a team, that Oliver was assembling, to take down the 33,1 project. Bart was given a costume and assigned the codename "Impulse"

In early 2007, Bart found himself back in Metropolis, where he saved Chloe's life and reconnected with Clark. During a mission to a LuthorCorp facility, Bart found himself captured and placed within a cell, where he was forced to run as fast as he could, or he'd be electrified. This was the first time that Bart tapped into the Speed Force, which attracted the attention of Black Flash. Bart was rescued from both the cell and the creature by Clark. Afterwards, Bart rejoined the team and departed Smallville, to take down the remaining 33,1 facilities.

About six months after Clark had made his debut as Superman, Bart sought him out. Together they went to Paris, where they fought the Brain and Monsieur Mallah, during which Bart once more found himself confronted by the Black Flash. Having informed Clark about this problem, Bart was taken to see Jay Garrick. Bart ultimately chose to confront the Black Flash, seemingly resulting in the demise of both him and the creature.