Onesimos was an Athenian red-figure cup-painter active c. 505–470 BC. He worked closely with the potter Euphronios and was one of the finest draughtsmen of the Late Archaic period. His name, meaning "useful" or "profitable", suggests he may have been of servile origin. He is known for large-scale compositions on the interior of kylikes, including the famous Ilioupersis (Sack of Troy) cup in Malibu.