There is little doubt that Caliban would have represented an exotic, semi-human, uneducated island-dweller to an Elizabethan audience, but it is harder to determine his racial origin. This is largely because he is first and foremost a character from Shakespeare's imagination which will have been influenced by stories about the unruly Irish, native Americans, Africans and a whole armies of non-Christian heathens. 

David Suchet played Caliban in an RSC production directed by Clifford Williams in 1978. In a quest to discover how he should play Caliban, Suchet undertook a detailed examination of Shakespeare's text. His initial scepticism towards the man-monster Calibans from earlier productions of The Tempest was rewarded with 'proof' that Caliban had to have a human form. Suchet unpicks Trinculo's first speech when he describes Caliban, 'A fish, he smells like a fish. . . a strange fish. . . his fins like arms. . . ' [II.ii.25-34]. 'I paused - 'fins like arms'. Shakespeare did not write 'arms like fins'. And I started to read the speech again and it became so clear to me that Shakespeare was not describing a fish-like man but a human being whose appearance, let alone his smell, was strange to Trinculo. . . Shakespeare had gone to great pains (not without tongue in cheek) to describe the popular concept of the 'native' (David Suchet: Caliban, Players of Shakespeare 1, Edited by Philip Brockbank, CUP, 1989, p. 171).