Prospero is the rightful duke of Milan. Twelve years earlier, he found refuge on this island after his younger brother, Antonio, seized Prospero's title and property. Prospero functions as a god on the island, manipulating everyone within his reach. He is helpless against his enemies until they appear on a ship nearby; but when they are close enough, he can use his magic to create a storm and bring them under his control.
Prospero's magic is the white magic of nature, not the black magic of evil men. This former duke of Milan is a complex personality. Although he refuses to free Ariel and enslaves Caliban, Prospero is really a beneficent ruler, never intending to injure even his enemies. Early in the play, Prospero appears callous and cruel, especially in his treatment of Ariel and Caliban. He is also autocratic in his treatment of Ferdinand, but Prospero realizes that Ferdinand and Miranda will value one another more if there are a few impediments to their courtship.
Prospero's humanity is clearly obvious in his treatment of Antonio, whom he calls traitor but whom he declines to treat as a traitor. Another example of Prospero's goodness is when he stops Alonso from apologizing to Miranda, telling him that there is no need for more amends. By the play's conclusion, it is clear that Prospero is just and fair, in addition to intelligent.