Bartholomew "Bart" Allen is a speedster from the year 2056 and the grandson of Flash (Barry Allen). When he came to the past, he joined the Team under the name Impulse. After Wally's death, he took on the mantle of Kid Flash. He later joined the Outsiders.
Given the dire situation that his time is in, Bart is serious and slightly jaded. But in order to win over the heroes of 2016, he adopted the persona of a hyperactive, vivacious and very talkative speedster, who was greatly appreciative of his extended family in the past. Whether accidental or intentional, Bart constantly "spoils" information for people, such as revealing Robin's and Nightwing's secret identities to Beast Boy, and that Iris-West Allen was carrying twins.
Bart and Nathaniel Tryon worked on a way to change the domination of Blue Beetle and the Reach. They believed that the cause of the apocalyptic event that made their time inhospitable started with the death of Flash, so Bart would travel back in time to stop it. Tryon, who as Neutron had been responsible for many past atrocities, gave Bart a special device that would strip Neutron of his powers. He also warned him that the time machine would break after using it once.
Bart's time machine arrived in the Mount Justice where he joyously greeted Nightwing, Robin and Beast Boy. He took the name Impulse and escaped them, starting a chase through the whole base. He was eventually captured by Nightwing.
Impulse was cuffed up and they interrogated the time traveler. Impulse received a glass of water from Nightwing, who wanted to acquire DNA of Impulse, which he noticed and gave his spit. Impulse soon revealed their secret identities to each other in an attempt to convince them he was a tourist from the future and the grandchild of Barry Allen, as they were surprised and skeptical of his claims. When Malcolm Duncan arrived and the door opened, Impulse phased through the cuffs and fled the headquarters.
Impulse arrived at the Allen house at the moment Barry Allen received a phone call about his supposed grandson. Barry initially denied the possibility, reminding everyone that he and Iris did not even have children, until Iris revealed that she was in fact pregnant. Impulse then greeted his unborn father and aunt, revealing to everyone that Iris was actually carrying twins, which surprised even her.
Wally arrived at the party after Nightwing called him. Bart greeted him with the same enthusiasm as he had given the others. Fully aware that Flash was supposed to die, he first attempted to prevent Iris from receiving a phone call from her boss about a rampaging supervillain. When that failed, he tried to dissuade Barry from going, saying that the Justice League could handle it. Flash went nonetheless, and Impulse followed. Impulse chased after the Flash saving him from hurting his derrière after getting hit by Neutron's omnidirectional energy waves. Impulse claimed that he wanted to see Flash fight in his prime. In a slip, he also revealed Neutron's name, and then to cover it up, claimed that Neutron was saying it all the time. They created a plan to stop Neutron: with Kid Flash's help, the duo created a large whirlwind around Neutron, causing him and his containment suit to detonate.
Neutron regenerated himself, being unable to stabilize his energy and was about to explode again. The Flash decided to carry Neutron to a nearby desert to save the city. Impulse knew that he could not reach it on time and tripped the Flash before he was caught in the explosion. Neutron detonated, but Kid Flash and Jay Garrick saved them both.
Impulse went back to the place where Neutron was again regenerating. Impulse applied the pill to him, which made him return to normal, with no memory of the events. When the speedsters came back, he lied to them and said that he did not know what happened to Neutron.
After Nightwing's DNA test revealed Bart's claims of his heritage to be true, Bart said he was ready to go back. But because the time machine was broken, he could not return. To maintain his cover, he feigned frustration at being stuck in the past, and claimed that he knew nothing about fixing time machines.
Because he could not return, he was taken under the care of the Garricks in Central City.
Since his arrival in the present Impulse has shown a personal interest in Blue Beetle. Blue Beetle was the first member of the Team Impulse almost immediately befriended and they have bonded further ("chill-hang"ed) during the course of the series. Later it is revealed that Impulse's main motive for keeping an eye on Blue Beetle is to prevent the Reach Apocalypse from occurring as it has in his timeline.