The head of ancient Egyptian sphinxes portrayed the reigning pharaoh but also, when featuring the head of a falcon, represented the sky-god Horus or Amun-Re, with the head of a goat. When the Greeks adopted the sphinx it became a female monster.
According to Greek legend the sphinx put a riddle to all who passed by and devoured those who failed to guess it. Getting it right meant the death of the monster a claim to the throne and the hand of Queen Jocasta. After many had died, one got it right: Oedipus.
What was the riddle that Oedipus solved?
The riddle that the sphinx put:
What animal walks on four legs in the morning, on two at noon, and on three at night?
Man, for in the morning, the infancy of his life, he creeps on all fours; at noon, in his prime, he walks on two feet; and, when the darkness of old age comes over him, he uses a stick for better support as a third foot.
Oedipus, a mythical Greek king, was the son of Queen Jocasta and therefore had to marry his mother.