The answer to the riddle of the Sphinx is 'MAN'. This riddle is an ancient Greek mythological story about a sphinx, a creature with the body of a lion and the head of a woman, who guarded the entrance to the city of Thebes. The sphinx asked a riddle to all who passed by, and anyone who could not answer it was killed. The riddle was 'What walks on four legs in the morning, two legs in the afternoon, and three legs in the evening?' The answer to this riddle is 'MAN', as a baby crawls on all fours, an adult walks on two legs, and an elderly person uses a cane for support.