In Act One of The Tempest, who stole Prospero's position?
Prospero’s brother Antonio conspired with Alonso to steal his position from him.
Prospero is a wizard or magic-user who is stranded on a deserted island with his daughter, Miranda. He used to be a duke, but his brother Antonio conspired against him with the king, Alonso, and shut him out. He pretty much then forced Prospero and Miranda onto a tiny boat and pushed them out to sea. Prospero’s friend Gonzalo took pity on him, helping him by bringing him food and his magic books so he would survive the journey. He did.
When Prospero creates a storm and Miranda begs him to stop, Prospero reminds her of all of this. It is not something he has ever forgotten.
My brother and thy uncle, call'd Antonio--
I pray thee, mark me--that a brother should
Be so perfidious!--he whom next thyself
Of all the world I loved and to him put
The manage of my state … (Act 1, Scene 2)
Indeed, Prospero has his opportunity for revenge. Alonso, Antonio, and Alonso’s son Ferdinand are shipwrecked in Prospero’s storm. He uses his magical servant Ariel to mess with them. She reminds them of what they did to him.
You are three men of sin, whom Destiny,
That hath to instrument this lower world
And what is in't, the never-surfeited sea
Hath caused to belch up you; and on this island
Where man doth not inhabit; you 'mongst men
Being most unfit to live. … (Act 3, Scene 3)
Miranda and Ferdinand hit it off. Prospero treats Ferdinand poorly, so that his prize will not seem too light, but Prospero is actually secretly delighted at the match. He also changes his mind about getting brutal revenge against Ferdinand's father and his brother. He decides they have suffered enough, and he forgives them. He does take back his kingdom though. His forgiveness has its limits, after all!