Pirithoüs (or Peirithoüs) was a king of the Lapiths and a close friend of Theseus. He was a son of Zeus by Ixion's wife Dia. The story went that when Zeus was attempting to rape Dia, he ran round her in the guise of a horse. His offspring was thus named for this incident, from peritheio, 'to run round' (peri, 'round' and theo or theio, 'to run'), as if his name was really 'Peritheüs'.