Ariel was freed from eternity stuck in a tree, of which he was imprisoned by the witch, Sycorax. If Prospero hadn’t come onto the island and freed him she would be stuck for eternity. Ariel has great magical power, so Prospero saw this and enslaved Ariel to help him seek justice, but he promises that once the work is done, he will liberate her, “I will discharge thee.”
Prospero was the duke of Milan, but was betrayed by his own brother, Antonio, and in love of his books and his thirst for knowledge lost his Dukedom. Prospero and Miranda were cast away on a boat, and left to die in mid-sea, by his brother! Luckily, they were drawn upon the shores of the island and survived.
All Prospero wants is Justice from what happened and his dukedom back, which he has the right to and deserves. The means of which he achieves these goals may seem power crazed but is justified, he has the chance to kill all those who took part in his outcast but does not, if he was a power crazed despot surely he would kill them, but all he does is make them apologise and give back what is rightfully his.
He manipulates all the characters into doing what he wants to, this may seem all about power, but the only reason he does it is to pull off his plan for justice. The only physical harm he causes is to Caliban, and this is only the way to really communicate with him, a power crazed despot would use more means to gain power, Prospero just uses his magic and knowledge to manipulate what happens.
Once Prospero achieves his goal of getting justice, and his dukedom back, he forgives all whom has plotted against him even those whom planned for his death, he does this even when he has the chance to kill or harm them all. This makes it clear that he is a wronged man seeking justice and not a power crazed despot other wise he would just crush them. He also sticks to his promise, he realises Ariel once her job is complete and also gives back the island to Caliban, a creature who raped his daughter.
All in all, the evidence given in the text points to him as a wronged man seeking justice.
