King Erichthonius (or Erechtheus) I of Athens was, according to some legends, autochthonous (born of the soil), and in other accounts he was the son of Hephaestus and Gaia or Athena or Atthis. According to Apollodorus, Hephaestus attempted to rape Athena but was unsuccesful. His semen fell on the ground, impregnating Gaia. Gaia didn't want the infant Erichthonius, so she gave the baby to Athena. Athena gave three sisters, Herse, Pandrosus and Aglaulus a small box and warned them to never open it. Aglaulus and Herse opened the box which contained the infant and future-king, Erichthonius ("troubles born from the earth"). The sight caused Herse and Aglaulus to go insane and they threw themselves off the Acropolis. Alternatively, Athena raised Erichthonius herself.
An alternative version of the same story is that, while Athena was gone bring a mountain from Pallena to use in the Acropolis, the sisters, minus Pandrosus again, opened the box. A crow witnessed the opening and flew away to tell Athena, who fell into a rage and dropped the mountain (now Mt. Lykabettos). Once again, Herse and Aglaulus went insane and threw themselves to their deaths off a cliff.
Erichthonius later became King of Athens and implemented many beneficial changes to Athenian culture. During this time, Athena frequently protected him. He founded the Panathenaic Festival in the honor of Athena. He taught his people to yoke horses and use them to pull chariots, smelt silver and till the earth with a plough.
He was sometimes said to be a snake with a human head. The snake was his symbol.
Erichthonius may have been the same person as Cecrops; scholars are divided. Some believe Cecrops was his son.