Timmy Baterman is one of the tertiary antagonists in Pet Sematary. In his life, he was a good normal man who went to war to fight the Nazis in 1941 and he was shot dead in Italy. He came back to the Ludlow town in a funeral box and his father, Bill Baterman, went insane when he got the news but soon after he quietened down because he knew of the cemetery in the woods and he knew what he would do.
Bill waited until the funeral of his son, then after the funeral he went back, dug up his son's corpse, and dragged it in a white bag up to the Pet Sematary. He was the first human that Jud Crandall knew of who decided to bury another human in the cemetery. But maybe not the only one.
Bill buried Timmy's corpse in the cemetery and then he went home and waited. Soon after, one night, he got a visit from Timmy. He was now Undead, and had walked through the dark woods to his house. Bill, believing that his son was now back alive again and perfectly normal, embraced his son delightfully and welcomed him back.
But what Bill didn't know, was that the burial ground was infected and possessed by the dark magic of the Wendigo and that through nefarious dark magic Timmy was now fully possessed by the Wendigo and absorbed all its knowledge. Although it looked like Timmy, the entity that was in Bill's house was the Wendigo and it began to dissolve into sadism over the next few weeks. In a few weeks, the possessed Timmy seemed to become one with the Wendigo, so it could act like Timmy on the surface and be creepily friendly with the townspeople, but at home he was a monster. Timmy was soon seen walking the streets of Ludlow, and scared people to death, as they knew that Timmy had died, having all gone to his funeral. So, Timmy was seen shambling along the streets, dishevelled and disorientated, although this was soon seen as a front because when spoken to Timmy was seen to be very conscious and aware of how to scare people. He asked a neighbour if she was free that night - presumably to rape her.
Timmy was now becoming an urban legend of Ludlow, and soon five men, Jud amongst them, went to Bill's house to talk to him. They noticed Bill had lost loads of weight and he was getting ill. He was also scared by the Wendigo, but he never talked to any of the men, other than to tell Timmy to be quiet. Timmy told George that his grandchildren were waiting for him to die so he could give them his non-existent heritage, he told Alan his wife was cheating on him, and enjoying it, and he told Jud and Hannibal something dark about their lives too that they were unaware of. Timmy seemed to be more than human and Jud finally realized that it was a demon inside of Timmy.
Timmy bid them all goodbye and chased them out of the place, laughing manically, but then Bill had finally had enough, and that night Bill soaked the house with oil, lit a match, and shot him and his Undead son in the head. When they were recovered, the doctor thought Timmy had been dead for months because of his decomposition.