What is Caliban?

Caliban confuses me because I don't know whether he is a man or a creature. And, I appreciate Shakespeare doing this characterization because it reflects the characters of Greek mythology that we read all last semester. Part of the beauty and mystery of and epic is disgusting who is man verses who is creature, who is good verses who is evil. Cal causes that same dilemma in each of us. At points we sympathize and empathize with him. Yet, at other points we see elements of his character that feel barbaric and ugly to us.