In Act III, scene 1, Ferdinand though a royal, serves as a willing slave to Prospero. He does this because he is in love with Miranda, saying:
The very instant that I saw you did
My heart fly to your service; there resides,
To make me slave to it
He performs Caliban's work of carrying logs, but does it without complaining, because of Miranda. When she offers to help him, he won't hear of it.
But if Ferdinand is a willing slave for Miranda's sake, she also promises to be his: "I’ll be your servant / Whether you will or no."
In the next scene, the action turns to Caliban, who, after drinking with Trinculo, and Stephano, claims to that he has been cruelly enslaved by Prospero against his will, "subject to a tyrant." He says the island is his, and, in fact, expresses the closeness he feels to the place that his been his home his entire life. From a post-colonial perspective, we can feel some sympathy for Caliban because of the way Prospero has treated him.