Speedsters have played a key role throughout the history of the Arrowverse, using their ability to time-travel to alter history. This tampering with time has also led to the creation of time remnants, time-displaced speedsters from divergent timelines caused by the alterations to main timeline. Rather than being erased from existence, these duplicate speedsters are preserved within the Speed Force and can appear alongside their original speedster source to avoid causing further temporal paradoxes.
Here are the most notable appearances of time remnants, with The Flash and Legends of Tomorrow featuring this trope prominently as the Arrowverse's timeline sees continued tampering from its time-traveling speedsters.
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Reverse-Flash
The most notable time remnant was Eobard Thawne, the Reverse-Flash who antagonized Barry Allen throughout his time as the Scarlet Speedster. While Eobard's ancestor Eddie sacrificed himself to prevent Eobard from killing Barry, all the changes that Eobard had made inadvertently made him into a time remnant as the alterations to the timeline he had caused were so profound, including causing the particle accelerator explosion that made Barry the Flash in the first place.
Since then, different remnants of Eobard has menaced Barry and his daughter Nora over the years, despite Eddie's death ensuring Eobard would never be born. Learning that his status as a living anomaly made him a target of the Black Flash to preserve the timeline, Eobard formed the Legion of Doom in Season 2 of Legends of Tomorrow to obtain the Spear of Destiny and make solidify his existence. Eobard would recruit scores of time remnants of himself across the timeline to ensure this though he was ultimately defeated. However, a handful of time remnants of Eobard still exist through divergent timelines and alternate worlds, sure to menace Team Flash in the future...or past.
Zoom
Team Flash's first major encounter against time remnants was perpetuated by the villainous Hunter Zolomon during Season 2 of The Flash. Hunter arrived under the guise of Jay Garrick, the heroic Flash of an alternate Earth who had become stranded on Earth-1. Instead, Hunter was secretly the villainous Zoom who intended to steal Barry and Wally West's speed for himself to grow even more powerful as he rampaged across the DCTV Multiverse.
Using a time remnant, Hunter made it appear as himself and Zoom were at the same places simultaneously to further his deception. To create the illusion that Jay had been killed, Zoom killed a time remnant of himself before the villainous truth about his plot was revealed, admitting it had been hard to convince a copy of himself to agree to be killed until the extent of his machinations were revealed. Learning of the concept of time remnants, Barry created one of himself to stop Zoom's plan to destroy the Multiverse and defeat him.
Savitar
In Season 3, Barry learned that the self-proclaimed God of Speed Savitar intended to kill Iris West. Later, Barry was horrified to discover that Savitar was a time remnant of himself, created to stop Savitar in an alternate timeline from killing Iris. While Savitar killed most of the army of time remnants, this version of Barry survived, though gravely wounded and sporting a grievous facial scar from the battle. Shunned by Team Flash for not being the real Barry in the wake of Iris' death, the time remnant would become Savitar himself, descending into villainy while forming a causal loop.
Barry would square off against Savitar multiple times across Season 3, with the villainous speedster recruiting Killer Frost to help him. After H.R. Wells sacrificed himself to save Iris' life, Barry and Savitar's final battle would result in Iris fatally shooting Savitar before he dissipated back into the Speed Force.
Airing Tuesdays at 8 p.m. on The CW, The Flash stars Grant Gustin, Candice Patton, Carlos Valdes, Danielle Panabaker, Tom Cavanagh, Jesse L. Martin, Danielle Nicolet and Hartley Sawyer.