He is the leader of the Saviors, a group of survivors who force other groups to give them half of their supplies, or make them suffer severely. One night, the Saviors ambushed Rick and his group after they had set up camp for the night while on their way to The Hilltop. After that, Negan brutally and savagely bludgeoned Glenn to death with a baseball bat covered in barbed wire that Negan called "Lucille". Realizing just how dangerous Negan really is, Rick unwillignly has his group live under the rule of Negan and the Saviors.
In an attempt to kill Negan, Carl infiltrates the Sanctuary, the Saviors' base, but is captured by the Saviors and taken prisoner. Negan tries to bond with Carl while he is held hostage, but it does not work out when Negan makes a joke about the gunshot wound to Carl's eye. When Rick and the group attempt to save Carl, Negan intercepted them and is about to tell them what he has done with the boy when Rick attacks him, only to discover that Negan has done "nothing" to Carl and that he is fine.
While Rick goes on a supply run, Negan goes to the Alexandria Safe-Zone to watch it while he is gone. There, he encounters Spencer Monroe, who tells him that Rick is not a suitable leader for the Safe-Zone and that when Negan kills him, Spencer will take over. Negan feels insulted by this and murders Spencer, saying that although Rick may hate him, he still has guts unlike Spencer, who he believes acted like a coward.
Afterwards, Negan sees the supplies gathered by Rick and demands it all, but leaves it in payment for Spencer's death. While Negan and some of his men are drivng back to the Sanctuary, they notice that they are being followed by Rick and a few others, resulting in a showdown. In the chaos, many of Negan's men are killed and Carl shoots off a portion of Lucille, causing Negan to develop a hatred for him. After Rick and his group are rescued, Negan retreats back to the Sanctuary, where he tells his fellow Saviors that they are the dominant force in the world and that they are going to war.