Tom is a yandere to Star Butterfly, from Star vs The Forces of Evil. He is Star's ex-boyfriend, and she broke up with him because of his short temper and controlling personality.
In "Blood Moon Ball", Tom invites Star to the Blood Moon Ball in an attempt to get her back. He plans to dance with her under the light of the Blood Moon, which is said to have mysterious powers that bind two souls together. When Marco interferes, Tom becomes enraged, and is about to kill him before Star uses her wand to freeze him.
Later on in the episode "Mr. Candle Cares", he sends one of his minions to pose as a guidance counselor at Echo Creek Academy. Mr Candle informs Star of her future as Queen of Mewni, which causes her to become rebellious. Marco discovers Tom's plan, and pretends that he and Star are going out. Tom reveals himself and takes him to the Underworld, where Tom proclaims he must kill him. However, Marco manages to persuade Tom in challenging him to a battle to the death. If Tom wins, Marco dies, but if Marco wins, Tom has to take him home and tell Star the truth. Both down to an agreement, they challenge each other to a game of ping pong. However, it turns out to be an unfair game, as Tom keeps beating Marco with his demonic powers. Soon, the two of them begin to talk about their thoughts on Star, like how she just does whatever she wants and makes up her own rules. While it is clear that Marco is not going to win the game, he points out that Tom will never win Star back no matter what he does. He cannot make Star be his girlfriend unless she wants to. Knowing that Marco is right, Tom takes him home.