Scythian dracanae

(Image taken from Riordan Wiki)

The Skythian Drakaina was the queen of the Drakaina who resided in what is modern day Ukraine.  According to the myth, the queen stole the Cattle of Geryon back to King Eurystheus in Tiryns to complete his tenth labor.  The queen refused to return the cattle unless Herakles agreed to mate her.  From their union three sons were born, Skythes, Agathrsos and Gelonos.

According to some accounts the Drakaina Herakles mated with was Ekhidna because Ekhidna was a Drakaina.  It is however unlikely that they were one and the same based on Herakles history with Ekhidna and her size.