Ariel is a spirit of the air who, because he refused to serve the witch, Sycorax, was imprisoned in a tree until rescued by Prospero. Ariel willingly carries out Prospero's wishes because he is eager to be free. Although he wants his freedom in exchange, Ariel approaches his tasks with enthusiasm, quickly doing what is asked and promptly reporting any activities that he observes. Early in the play, Ariel reports the plot to murder Prospero, and later, he assists in punishing Prospero's enemies. Ariel's obedience is an important symbol of Prospero's humanity, because he ameliorates Prospero's role on the island and humanizes the action that Prospero takes against his old adversaries. Finally, Ariel's willing obedience of Prospero's wishes stands in stark contrast to Caliban's cursing and plotting against the same master.