Story

A warrior identical to Goku who attacked Trunks' parallel future timeline.
This fiend was created when Zamasu, an Apprentice Supreme Kai from Universe 10, took control of Goku's body in another timeline.
Convinced that mortals are a mistake and unworthy of ruling their own universe, he sets out to destroy all life as part of his twisted sense of justice.

(Dragon Ball Super Chapter 14)

He kills his former master, Supreme Kai Gowasu, and steals his Ring of Time, a tool that allows the Supreme Kais to travel between parallel timelines. He discovers Future Trunks' timeline where the Supreme Kai and God of Destruction had already passed away and heads there to destroy it, thereby becoming its one and only god.

Trunks fights back to defend his world, leading to a fierce back and forth battle between the two fighters. Before Goku Black can deal the final blow, Trunks escapes to the past again in the time machine his mother built.

(Dragon Ball Super Chapter 16)

Trunks enlists the help of Goku and Vegeta and brings them back to his timeline.
Goku Black has an intense battle with Vegeta, during which he transforms into a Super Saiyan.

(Dragon Ball Super Chapter 19)

Vegeta unleashes a rage-powered attack, but Goku Black manages to deflect it with a Barrier.
The tides change once Vegeta transforms into his Super Saiyan God Super Saiyan form, and the power-hungry destroyer finds himself overwhelmed by the Saiyan prince.

(Dragon Ball Super Chapter 19)

Just when it looks like Goku Black is going to meet his end from a full power Final Flash attack from Vegeta, another Zamasu- this one from Trunks' timeline- suddenly appears and rescues him.
It turns out the two former Supreme Kai trainees made a pact to put the Zero Mortal Project into effect.

(Dragon Ball Super Chapter 19)

The duo proves to be formidable, with Zamasu using his restorative powers to heal any damage taken by Goku Black, triggering the latter's Saiyan cells and giving him a dramatic power up each time.
After this jump in power, Goku Black gains the Super Saiyan Rosé transformation and uses it to overpower Vegeta, who is no match even in his Super Saiyan God Super Saiyan form.

(Dragon Ball Super Chapter 20)

Goku and Vegeta retreat temporarily to their timeline in the past.
Goku Black and Zamasu realize that their Zero Mortal Project has been discovered by the Supreme Kai in the other timeline and make plans to leave this Earth and head to another planet.
However, before they depart, they begin eliminating all the remaining mortals on Trunks' world.

(Dragon Ball Super Chapter 21)

After training in the past, Goku and Vegeta return to Trunks' timeline for a rematch.
Vegeta once again takes on Goku Black, this time starting off in a weaker Super Saiyan God state. Goku Black mocks Vegeta at first, but finds himself being driven back as Vegeta strategically transforms into Super Saiyan God Super Saiyan only in bursts just as he attacks.

(Dragon Ball Super Chapter 22)

In the face of this dire dilemma, Goku Black and Zamasu use the Potara to fuse and become the even more powerful Fusion Zamasu.

(Dragon Ball Super Chapter 22)

First Appearance

"Dragon Ball Super" Chapter 14

Transformations

Super Saiyan
Goku Black's hair turns a golden color and he transforms, drastically increasing his strength.
He uses this transformation while fighting Vegeta.

Super Saiyan Rosé
Goku Black's transformation that surpasses the level of Super Saiyan God. His hair in this form changes to a light pink color rather than a blue hue. This is a special transformation that is unachievable by normal Saiyans; Goku Black can only achieve it because he possesses a Saiyan body and a divine spirit.

Trivia

He's so cruel that he attacks his own master three different times!

Goku Black turns a deaf ear when a Gowasu from another timeline tries to convince him to stop his evil ways and uses a blade-shaped Ki attack on his well-meaning teacher without hesitation. And this is in addition to murdering the Gowasu he knew in his own original timeline to get the Ring of Time and killing the Gowasu that existed in Future Trunks' timeline!

(Dragon Ball Super Chapter 21)

Scroll down to the comments for a hint about who next week's character will be!

*All comic images are from the Japanese version.