The Flash from the Future
Impulse, great-grandson of Barry Allen, may have the greatest potential of any Flash, but without a mentor to train him that potential has gone untapped.
He is also an inventive genius. He claims to have created his own time-machine, which used to travel back to the present day for an unknown purpose.
Bart Allen arrived in the present shortly after the death of Wally West. He quickly sought out each of the Flashes who all refused to train him. He then joined the Teen Titans and was able to learn a few tricks of the speedforce, especially during fights with Captain Boomerang Jr who was an occasional enemy of the Teens. Impulse is now the oldest member of the Teen Titans, and acts as the team’s leader.