Pelias was the twin son, with Neleus, of Poseidon and Tyro. A story told by Apollodorus describes how as a baby he had been suckled by a horse that had trodden on his face and bruised it.

This explains his name, from pelios, 'discoloured by a bruise', 'livid'. (Other accounts say a mare kicked him, but the result was the same.) For a name of similar origin, see Pelops.