Garazeb Orrelios, called Zeb, is a Lasat from Lasan, a former captain of that world's High Honor Guard, and the muscle of the Ghost crew in Star Wars Rebels. He appeared first in the 2014 tie-in books Rise of the Rebels and Zeb to the Rescue, and is voiced throughout the series by Steve Blum.
Genocide, stated plainly
The Empire cleared Lasan using T-7 ion disruptors, weapons whose effect on a living body the show describes but never shows. Hera Syndulla spells it out to Sabine in the first season: very few Lasat survived, and none remain on Lasan. Zeb spends the early episodes believing he is close to the last of his species, and his hatred of the Empire is not political. It is specific.
Lira San
The season-two episode "Legends of the Lasat" is the payoff, and it is the most unusual thing Rebels ever did. Following a piece of Lasat prophecy, Zeb pilots the Ghost through a collapsing star cluster by feel, and finds Lira San — the Lasat homeworld before Lasan, populated by millions of his people. The show does not undo the genocide. It simply establishes that his species will continue, which is a different and better kind of relief.
The double act
His running feud with Ezra Bridger is the crew's comic engine, and his eventual friendship with the Imperial agent Alexsandr Kallus — the officer who was present at Lasan — is the series' most patient redemption arc, built across four seasons out of two men who begin by trying to kill each other.