Caliban is this being who is the son of a witch. He is described as a monster -- he looks really horrible. Prospero is an Italian nobleman who has enslaved Caliban by using magic.
Caliban hates Prospero very much. When he sees Stephano and Trinculo, he initially thinks that they are more spirits sent by Prospero to torment him. But then, after they get him drunk, he decides that Stephano is a god. He decides that he decides that he will become Stephano's servant. He will serve Stephano and he hopes Stephano will help him kill Prospero.