1) Caliban is initially presented kindly by Prospero, but after attempting to assault Miranda, is made Prospero's slave and seen as a monster.
2) Prospero describes Caliban's mother Sycorax as a "foul witch" and "blue-eyed hag", casting her in a negative light, though we only have Prospero's perspective.
3) Caliban's interactions and statements can be interpreted differently based on how the actors portray his emotions - whether regretful or unrepentant - leaving Caliban's character more ambiguous.