Dr. Gregory Butler

Dr. Gregory Butler is a tritangonist that appears in Happy Death Day, and the main antagonist in the Happy Death Day 2U.

Happy Death Day
He is seen teaching in his class and when he is about to leave, Tree will visit him because they have an affair on Stephanie's coast. However Lori also had feelings for him, and was upset with Tree, and because of that, what time cycle began, with Tree finds out and the two fight, and Lori dies. Tree also ends his relationship with Butler.

Happy Death Day 2U
In this altenative timeline, unlike other timeline, Butler does not relate to Tree but to Lori, but when his wife discovers this during a discourse that Tree saw. Butler and his wife plotted together to eliminate Lori, so he releases John Tombs to kill Lori. Tree then realizes that Dr. Butler is Lori's real killer, and he then reveals himself to Tree and his friends, however in the confrontation, Stephanie appears revealing that she is Butler's accomplice and shoots Lori, he attacks Tree again, and when Stephanie gives her a gun, he then cheats on her by shooting her saying he wants a divorce.

And when Butler is close to killing Tree, Carter appears and distracts him so that Tree can escape and her chases her into an exam room magnetic resonance, and when Butler was close to killing her, Tree then turns on the magnetic machine. Butler is strapped to the machine and stabbed to death with a screwdriver by Tree.