A devil, a born devil, on whose nature
Nurture can never stick; on whom my pains,
Humanely taken, all, all lost, quite lost;
And as with age his body uglier grows,
So his mind cankers. I will plague them all,
Even to roaring.
– William Shakespeare
The Tempest, Act 4, Scene 1. Prospero calls Caliban a born devil and no amount of education or nurture can change his basic nature. And as he grows older, his body as well as his mind grows uglier. This speaks to the colonizer mentality Prospero holds in that he sees creatures like Caliban as inferior beings who need to be civilized. Prospero vows to put Caliban and his fellow plotters Stephano and Trinculo in agony until they roar in pain.