Hephaestus and that of the son of Dardanus and Batia who married Astyoche and was the father of Tros. For the first Erichthonius there are several popular origins.
One is to derive his name from eris, 'strife' and chthon, 'earth' with reference to the strife between his father Hephaestus and Athena: the story went that Hephaestus embraced Athena and made to possess her but she pushed him away and his semen fell on the earth.
According to another version of this incident Hephaestus ejaculated against Athena's thigh when she pushed him away and in disgust she wiped off the semen with a piece of wool (erion), which she then threw to the ground (chthon).
Another explanation of his name derives it from eri, 'very', 'much' and chthon 'earth' in the sense 'plentiful land', a suitable name for a king. But perhaps his name is really just an expanded form of Erechtheus. The two are sometimes confused. The second Erichthonius above was reputed to be very wealthy and to own three thousand mares: for him the 'plentiful land' definition seems best.