Pirithous is the son of Ixion, king of Larissa in Thessaly and half-brother to the centaurs. Though of kinship with the centaurs, he finds them and the circumstances surrounding their conception abhorrent. Pirithous has some of his father's brutality and rashness, particularly where the centaurs are concerned, as evidence by his punishment of Eurytus and his later scapades with Theseus. Nonetheless, though quick to anger, in his calmer moments he demostrates considered counsel.
Pirithous and his kingdom Larissa are diametrically opposed to Pelias and Iolcus, particualrly on account of Pelias' support for the centaurs. But Larissa is not powerful enough to wage open war with Iolcus. There is an uncomfortable truce between the two realms.
Theseus is a friend of Pirithous, and will become more so, resulting in a dangerous alliance between the two in the future.