Echidna was a half-woman, half-snake creature in Greek mythology. She is also known as the "mother of all monsters", as she gave birth to most of the Greek mythical creatures. She was the wife of Typhon, who was the "father of all monsters" and the most fearsome and dangerous monster in said mythology.
Both she and her husband were the children of Gaia and Tartarus. After seeing Zeus kill and capture most of her children, Gaia mated with Tartarus and produced the mighty and terrible Typhon, whom was tasked of destroying the Olympian gods. He then sought to mate with Echidna in order to produce a legion of terrible monsters to help fight against the gods.
The couple attacked the Olympians, but Zeus managed to repel them, burying Typhon under Mount Etna. Echidna and her children, however, were spared to continue challenging future heroes. Echidna was later killed by Argus Panoptes while sleeping and her corpse remaining in her cave ever since.
Echidna and Typhon bore many children, but none were was famous as they. The first was Orthrus, the two-headed dog that guarded the cattle of Greyon. Secondly was Cerberus, the three-headed hound who guarded the gates of the Underworld. The third was the Lernaean Hydra, the multi-headed serpent that grew two heads if one was cut off. The Gorgon sisters, the best known being Medusa. And lastly the Chimera, a creature that had the heads of a lion, a goat and snake.