The Walking Dead’s Morgan Jones is a severely damaged person, as anyone who witnessed his undead wife bite and kill his son might be. The psychological damage of that can do an intense number on a person. To wit: In season three, Morgan loses his grip on sanity and falls under the belief that he must “clear” all zombies. After Rick pays him a visit, and Morgan very nearly kills his old friend, Morgan decamps and continues his zombie-killing spree. He also kills two men without remorse before he finally meets Eastman, the cheesemaker.
In a manner of speaking, Eastman sobers Morgan up. He rids Morgan of his bloodthirst. He vanquishes Morgan’s addiction to killing. It was a good run for Morgan, too. He maintained his murder-sobriety for a long stretch, until the sixth season finale of The Walking Dead when he shot and killed a Savior who had tried to kill Carol. Perhaps recognizing that his itch to kill was returning, Morgan decided for another change of scenery, moving to The Kingdom.
However, after Benjamin’s death late in season seven, Morgan falls off the wagon again. He reverts to his state of insanity fueled by PTSD. He joins the All Out War, and he transforms into a killing machine. He feels invincible. He kills Richard. He slaughters Saviors by the dozen. He nearly kills Jesus. He wants to “clear” again.