From a game called I.Q. Challenge, a brain teaser:
A boy is captured by a cruel master who tells him he will have to become a servant to one of his two sons, Theo the Terrible or Angus the Awful. The boy is determined to escape such a punishment. The master gives the boy one chance to make a single statement that will decide his future. If what he says is true his is to serve Theo the Terrible, but if what he says is false he is to serve Angus the Awful. What does the boy say to earn his freedom?
The answer is posted in the comments.