The New 52 (2014)
Wallace's introduction came during the Future's End event, which involved a cascading sequence of flash-forwards to alternate timelines and possible futures. Wallace started out dead, his story uncovered by a Barry Allen seventy years in the future, then was empowered by an encounter with the Flash and ultimately driven to sacrifice himself five years in the future, and ultimately empowered by his future self and the effects of time travel in the present day.
As a teenager with Speed Force abilities, Wallace tried to hone his new skills both on his own and at the slightly arms-length mentorship of the Flash, who he only knew in his Super Hero identity, rather than in his civilian life. Wallace's first act with his abilities was to save a schoolmate from bullies, but in doing so heavily implied that his powers were actually connected to the New 52 incarnation of Reverse Flash, Daniel West.
However, before that mystery could be explored too heavily, Wally West -- the original Kid Flash -- returned from an extended time trapped in the Speed Force, setting in motion the continuity-altering events of Rebirth (DC UNIVERSE REBIRTH #1, 2016).
Following Wally's return, Wallace was taken under Barry's wing more completely, though he hesitated to share his secret identity with him at first, which made things infinitely more complicated for Barry, considering Wallace's close connection with his aunt, Barry's girlfriend Iris West.
In this version of events, Wallace's Speed Force powers were related to -- or rather, galvanized by -- a massive Speed Force storm which struck Central City and empowered hundreds of people at random. Centers to help people adjust to their new abilities began popping up and Barry, as the Flash, took notice of Wallace's presence. Barry, as the Flash, took Wallace in, but continued to keep his identity and their out of costume relationship to one another a secret.
Eventually, Wallace learned the truth about his "cousin," Wally West, who had returned from the Speed Force. Wally had been the "original" version of the character and Wallace, after speaking, came to briefly worry that he was some sort of aberration caused by time travel and the overlap of different threads in the multiverse. Wally assuages these fears, however, by insisting that he and Wallace are family.
Eventually, the secrets surrounding Wallace's life began to reveal themselves. First, he learned that his mentor the Flash and his aunt's boyfriend, Barry Allen, were in fact the same person. Then, he learned that the man he believed to be his uncle, Daniel West, the third Reverse Flash, was actually his father. Shocked and betrayed, Wallace went on a quest for answers about his father where Wallace learned from Captain Boomerang that, despite Daniel's past, he died a hero sacrificing himself to save innocent lives (FLASH #18-19, 2017).
Around that time, Wallace joined two new teams, the Teen Titans lead by Damian Wayne, the current Robin, and Defiance, a team put together by a "reformed" Slade Wilson aka Deathstroke, who had previously attempted to use Wallace's speed force powers to travel back in time and revive his own son (in 2017's "The Lazarus Contract" storyline). While the Teen Titans had seemed to struggle under Damian Wayne's domineering (but usually harmless) lead, Defiance performed more like a boot camp run by Slade's sometimes brutal methodology. Still, Wallace excelled in both arenas, even when he risked spreading himself too thin.
During the events of 2018's "Flash War" storyline, Wallace is taken to a version of the Future where he did not exist, which reawakens his old fears about being an anomaly created by the time warping caused during 2011's Flashpoint event Barry sparked. This drove a wedge between Wallace and his mentor, which they are still working to repair ("Flash War", 2018).