Echidna is part of Greek mythology. The Marvel adaptation was created in 2014 by Cullen Bunn and William Sliney. Making her first appearance in issue #11 of the 1st volume of the Fearless Defenders comic book series.
Echidna is the granddaughter of Set, an Old One. Born to his son Phorcys who mated with Ceto, a sea monster. She has sired many of the monsters of Greek mythology, most of which the heroic demi-god Hercules has battled. Most of them were sired with Typhon, one of the Titans. Except for Angerboda who she sired with Varcolac and the Snakes of Many Colors.