Goku Black

Goku Black (ゴクウブラック, Gokū Burakku) is an evil entity from Future Trunks' timeline who calls himself Son Goku. He is actually Zamasu from an unaltered main timeline, in which he stole the body of the original present Goku and sought to destroy all mortals alongside the Zamasu originally from Trunks' timeline. He appears as a playable character in Dragon Ball FighterZ, and can also enlist the aid of Zamasu.

Background
A Supreme Kai-in-training from Universe 10 named Zamasu takes it upon himself to purge mortals in his misguided effort to protect the multiverse. As part of this plan, he uses the Super Dragon Balls to switch bodies with Goku, using the Saiyan hero's immense power with his own godly abilities to carry out the genocide of all mortals as the dark savior, "Goku Black".