At the beginning of the play, the audience's reactions to Prospero are rather ambivalent, to say the least. He is verbally abusive towards Ariel when his authority is challenged, and threatens him with torture that seems to present him almost as a dictator who will not stand to have his authority questioned in any way. Note what he threatens to do to Ariel:
If thou more murmur'st, I will rend an oak,
And peg thee in his knotty entrails till
Thou hast howled away twelve winters.
This punishment seems to be even worse than the punishment Ariel suffered under Sycorax, who had control of Ariel before Prospero's arrival. However, by the end of the play, Prospero is willing to free Ariel and give up his magic in order to return to the world of men and take up his position as the Duke of Milan. He sets everything back on its course and makes everything alright once again. In the play, he shows himself as a man who uses his power to have total control over what happens on the island. By the end of the play, he is willing to announce that power in order to return to civilisation and to give his daughter a future. This points towards at least some level of moral transformation within his character.