Goku Black (ゴクウブラック Gokū Burakku), usually referred to as Black, is the main antagonist of the “Future” Trunks Saga of Dragon Ball Super. His true identity is Zamasu (ザマス Zamasu) from the unaltered main timeline within Universe 10. He is a former North Kai and Supreme Kai apprentice serving his former master Gowasu.
Goku Black visited Universe 6, went to the Super Dragon Balls from the unaltered main timeline within that universe, summoned Super Shenron from said timeline, wished to switch bodies with Goku from the unaltered main timeline within Universe 7, and Super Shenron granted Goku Black’s wish. Goku Black sought to destroy all mortals alongside Future Zamasu. He was then given the name “Goku Black” by Future Bulma when he initially referred to himself as Goku.
It was revealed in an interview with Akira Toriyama that the inspiration for Goku Black originated from the “copy of the hero” idea in media such as “False Ultra Man” of the Ultraman series or “False Kamen Rider” of the Kamen Rider franchise.