There is an interesting love/hate feeling for Caliban throughout the play. While on one hand he tries to rape Miranda and the audience are therefore led to despise Caliban, on the other hand the audience are supposed to feel pity for Caliban, as he himself has been usurped from his island and get treated rather badly by the majority of the characters within the play.
Interestingly the reader never really gets a good idea of what Caliban looks like, the descriptions of him within the play are lacking in detail, and most of those descriptions are given by Characters who despise Caliban, and therefore cannot be reliable anyway. The descriptions range from "tortoise", "fish" and "beast". He is also described as a "mis-shapen knave" who is "as disproportioned in his manners/ As in his shape" Again however, this could just be malicious talk from Prospero.
Caliban's name is actually an anagram of cannibal, in the time when The Tempest was written, cannibal was spelt 'canibal' perhaps Shakespeare intended this.
There are also two sides to Caliban's intellect, there is on one hand the argument that Caliban must be less intelligent than characters such as Stephano and Prospero for him to be a slave to them, but on the other hand, Shakespeare has given Caliban some of the most poetic language;
"Be not afeard, the Isle is full of noises,
Sounds, and sweet airs, that give delight and hurt not:
Sometimes a thousand twangling instruments
Will hum about mine ears; and sometimes voices,
That if I then had wak'd after long sleep,
Will make me sleep again, and then in dreaming,
The clouds methought would open, and show riches
Ready to drop upon me, that when I wak'd
I cried to dream again."
Not only doe's Caliban speak the most...