The Groom

The Groom is a rare undead monster added in 1.0.4. He has 200 hp, 14 damage, and 8 defense. When killed he has a 100% chance to drop a top hat. He's simply a stronger zombie with a hat. He is more commonly found during a Blood Moon.

Trivia

 * 1.0.4 Due to a bug, he would not spawn

The fact that he is an undead, 'Groom' may be a joke referencing the "Corpse Bride" story or the Jewish folklore in which it's based. It could also be referencing the movie "Kill Bill" where the protagonist is named "The Bride" and she was thought to be dead.
 * 1.0.5 The Groom was reinstated into the game, bug free.

It is similar to Tim and Doctor Bones in the sense that they all drop hat vanity items