Zamasu

Zamasu is a major antagonist in the Future Trunks Saga of Dragon Ball Super. He appears to be working alongside Goku Black to kill all of the mortals.

Zamasu is the apprentice of Gowasu, the Supreme Kai of Universe 10. He holds an incredibly black and white viewpoint believing that the gods are all good, whereas mortals are evil and need to be wiped out for the good of the Universe.

History
Goku first encounters Zamasu chronologically when he, Beerus and Whis go to see him and his master, Gowasu. Goku spars with Zamasu and defeats him. He offers his hand to Zamasu but the latter refuses. Zamasu's defeat at Goku's hands would only further his hatred of mortals. Zamasu later suggests to Gowasu that they wipe out the primitive and violent mortals on the planet Badari. Gowasu, however, states that only the God of Destruction can carry out that act. Gowasu then uses the Time Ring to allow him and Zamasu to travel to the future of Badari. He also gives Zamasu an earring that makes him a Kaioshin, as apprentices cannot go.

The two fist bump and say "1000 years", transporting them to the future of Badari, where the planet's natives are fighting each other. This only serves to further Zamasu's belief that mortals are all bad. A Badari attacks the two Kais, but Zamasu slices it in half.

Returning to the future, Zamasu returns the earring Gowasy loaned him and debates his master on whether they can learn from mortals.

Zamasu later appears in Future Trunks's timeline. Curiously, this Zamasu was wearing a green earring instead of a pair of orange ones, suggesting that he is from the future. Zamasu reminded when Goku Black is about to use his Black Kamehameha, reminding Black of his promise to allow him to kill Goku.

Powers and Abilites
According to Goku, Zamasu's power surpasses the power of Universe 7's Supreme Kai.

His future counterpart can fight on par with Super Saiyan Blue Goku when he is at full power, as well as stand his ground against Super Saiyan 2 Future Trunks.