The Kerkopes, Akmon and Passalus, were two robber dwarves.
Heracles met the Kerkopes, and because they wanted to rob him, hanged them on a stick behind his back. The Kerkopes then told Heracles that his bottom was black because it was in the sun for so much time. Heracles, humored by the dwarves, let them go because they were funny. However, Zeus turned them into monkeys.