The Original Riddler Picture

"What is that which has one voice and yet becomes four-footed and two-footed and three-footed?" - Apollodorus, Library 3.5.8.

The Sphinx was famous for its riddle enounced above. The Greek is from the Perseus website linked to (please don't comment in Greek, my knowledge is just enough to find the right passage in the Perseus text, not to understand it properly). The answer should be well known, though I won't give it away here. The hero Oedipus could answer it, when he met the Sphinx on his road to Thebes, causing the poor, frustrated creature to kill itself.

This statue is known as the Naxian Sphinx and stands in the Museum of Delphi, Greece. It is about ten meters (ca. 30 ft.) high. It dates to the 6th century B.C.
Continue Reading: Thebes