Who He Is At First:
By the time Season 6 of The Walking Dead rolled around, spectators thought they had seen it all. Then along came Negan (Jeffrey Dean Morgan), who made the Governor (David Morrissey) look like Mary Poppins. Negan is the leader of group called the Saviors. He rules with a Machiavellian fist: Anyone who betrays him is sentenced to a public and painful death.
Negan has an endless appetite for violence. In the name of survival, he is willing to take out whoever gets in the way of his authority. In the Season 6 finale and into the Season 7 premiere, Negan captures Maggie (Lauran Cohen), Rick (Andrew Lincoln), Daryl (Norman Reedus), Glenn (Steven Yeun), Michonne (Danai Gurira), Rosita (Christian Serratos), and Abraham (Michael Cudlitz). He tells them that he owns them now, but they must pay for harming his people. One person from Rick's group must feel the full punishment of his spiked bat Lucille.
The vindictive Negan enjoys the game of deciding his victim, choosing with "eeny, meeny, miny, moe." He lands on Abraham and pummels him with Lucille. Daryl tries to stop him and that leads Negan to bludgeon Glenn while his wife Maggie watches helplessly.
Who He Becomes:
(SPOILER ALERT!) If you're not caught up with Season 10, do not continue!
Rick eventually captures Negan. Instead of doing away with him, Rick decides to hold him prisoner. Negan spends the next several years locked up in a jail cell in Alexandria. Over that time, he seems to enjoy not having to be a sadistic animal. He offers advice to people and even befriends Rick's young daughter.
Negan doesn't want to leave Alexandria, but he has to escape because the townspeople think he murdered someone. He joins the Whisperers and uses his master manipulation to woo Alpha (Samantha Morton). Negan secretly works with Carol (Melissa McBride) to Alpha. In the end, he saves the group from being destroyed by the Whisperers.