Sphinx

Apollodorus gives the fullest surviving account of the Sphinx: a creature with the face of a woman, the breast, feet, and tail of a lion, and the wings of a bird, sent to plague Thebes. She took up a position on a hill near the city and put the same riddle to every traveler who passed: what has one voice and yet becomes four-footed, two-footed, and three-footed? Whoever failed to answer, she killed on the spot, and the deaths mounted until the city was desperate for a solution.

The riddle's answer, per Apollodorus, is a human being: crawling on all fours as an infant, walking on two feet as an adult, and adding a cane as a third support in old age. Apollodorus credits a stranger named Oedipus with working this out; solving the riddle broke whatever power kept the Sphinx alive on failure, and rather than accept defeat she threw herself from the citadel and died. The vacant Theban throne and the widowed queen Jocasta both passed to Oedipus as his reward - the marriage that sets the rest of his own story in motion, though that story belongs to Oedipus rather than to the Sphinx's own myth. The encounter itself is told in Oedipus and the Sphinx.

The Sphinx's design - a human head on a lion's body, sometimes winged - closely parallels figures from Egyptian and Near Eastern art centuries older than any Greek telling, and most classicists treat the Greek Sphinx as an import that picked up the riddle and the Theban setting only after arriving in Greek storytelling. Unlike the silent, monumental Egyptian sphinx built as a guardian statue, the Greek Sphinx talks, kills, and eventually loses - a living antagonist inside someone else's hero story rather than an architectural fixture. Diodorus Siculus describes the Syrian goddess Derceto of Ascalon with a woman's head and a fish's body, a Near Eastern hybrid unlike any Greek fish-tailed woman.