Caliban is certainly one of the most intriguing characters in this play. He is variously abused and insulted by the other characters, but we learn most about his background from Prospero, whose prejudice is self-evident. Note how he refers to Caliban as "Thou poisonous slave, got by the devil himself / Upon thy wickend dam." Although Prospero and Caliban, by Caliban's own ackowledgement, at first were friends, his attempt to rape Miranda quickly ended that. Caliban interestingly does not attempt to deny this charge, merely bemoaning his lack of success, dreaming about "peopling" the island where the play takes place "with Calibans."
Caliban is thus enslaved by Prospero. However, he is also deceived and enslaved in similar way by Stephano and Trinculo. Interestingly, his motives for committing murder are clearly shown to be not as terrible as the plan to kill of Antonio and Sebastian, offering an interesting moral comparison.
Thus, when we consider Caliban, we see that he is exploited and abused by other characters. Whilst we can definitely say his actions show he deserves some of this treatment, at the same time we might emerge feeling more sympathy for Caliban than for other characters. Interestingly, many modern productions cast him in a very sympathetic light, using Caliban to comment upon the evils of colonialism.