Answer: The Riddle of the Great Sphinx
Explanation: As per the greek legend, there was a Sphinx eating people who could not answer the riddle correctly: "What is the creature that walks on four legs in the morning, two legs at noon and three in the evening?". The answer to it is "the man" because when he is a baby he would crawl on all fours, then when the man learns how to walk he does it on two legs and finally on three when the man is old and needs a cane to walk. The hero Oedipus answered correctly and the Sphinx was killed.