Described in the character list as "a savage and deformed slave," Caliban is the son of Sycorax, an evil witch who has since died but who once held sway over the island now ruled by Prospero. Regarding him as a "beast" and a "poisonous slave, got by the devil himself' upon Sycorax, Prospero has forced Caliban into servitude (IV.i.140; I.ii.319). By contrast, Caliban considers himself mistreated and overworked. He bitterly accuses Prospero of befriending him in order to take advantage of his gratitude and rob him of the island which he considers his birthright.

Eventually Caliban begins to plot against his master and persuades Stephano and Trinculo to try to murder Prospero; but the plot is foiled by Ariel in IV.i, and the three conspirators are punished with cramps, pinches, and convulsions.

At the close of the play, Caliban repents his plot against Prospero and regrets his foolish admiration for Stephano: "I'll be wise hereafter," he declares, ''And seek for grace. What a thrice-double ass / Was I, to take this drunkard for a god, / And worship this dull fool!" (V.i.295-98).