Erechteus

Perhaps the same character as Erichthonius, or his son or grandson. He had a snake's tail and was raised in the temple of Athena by the goddess herself. He then became king of Athens.
When Athens and Eleusis were at war, the oracle of Delphi told him his city would win the war if he sacrificed one of his daughters. One of them volunteered immediately.
According to another version king Cecrop's daughter Aglaurussacrificed herself. Either way, Eleusis was defeated and became part of Athens.