The Groom

There is no item that summons him. Blood Moons are the usual source and he is rare even then, but a Graveyard produces a slow trickle of him at any hour of any day, which is a great deal easier to plan around than waiting for the night sky to turn. He moves and attacks like an ordinary zombie, so he is never a threat on his own. The danger is that he arrives in the middle of everything else a Blood Moon throws at your door.

He and The Bride are the only enemies in the game whose spawn rate climbs when your luck is bad, and the Bloody Tear drop follows the same rule. If you are hunting him on purpose, deliberately tanking your luck is the fastest route there, which is the reverse of nearly every other farm in the game. Anything you would normally drink or place to improve your odds is working against you here.

The Top Hat is his signature, and since the other two Tuxedo pieces are crafted from Silk and Black Thread, one lucky kill finishes the whole outfit. The Bloody Tear matters more in practice, because it lets you start a Blood Moon whenever you feel like it rather than waiting for one, which makes him the seed of his own farm. His bestiary entry and banner also complete in a fraction of the kills most enemies demand, so the collection side of him is quick.

A throwaway Discord line about the Angler being an orphan turned into a fan theory that he and the Bride are the Angler's parents, which Redigit then declared canon, also as a joke. His achievement name is a clipped wedding vow. He also predates the Bride by a very long stretch, which is why he owns the achievement and she does not.