Echidna

Echidna (Έχιδνα in Ancient Greek, meaning "she viper") is the daughter of Phorkys and Ceto and is considered the mother of all monsters. Typhon is her husband. Percy, Annabeth, and Grover encounter her in The Lightning Thief on the top of the St. Louis Arch. Her children include:


 * Nemean Lion (killed by Percy in The Titan's Curse during the Battle in the National Air and Space Museum in Washington, D.C)
 * Ladon
 * Chimera
 * Sphinx
 * Hydra (killed by Percy, Annabeth, and Grover in The Lightning Thief film while they were in the replica of the Patheron in Tennessee)
 * Cerberus (giant mixed-ruff weiller-hellhound found in the Underworld and guarding way to the living from the dead in Hades's Underworld; first appeared in The Lightning Thief film when Percy, Annabeth, and Grover go to the Underworld to speak to Hades)
 * Orthrus
 * Ethon
 * Crommyonian sow
 * Colchian dragon
 * Clazmonian Sow

History
Echidna was described by Hesiod as a female monster spawned in a cave, who mothered with her mate Typhon almost every major horrible monster in the Greek myths,

''The goddess fierce Echidna who is half a nymph with glancing eyes and fair cheeks, and half again a huge snake, great and awful, with speckled skin, eating raw flesh beneath the secret parts of the holy earth. And there she has a cave deep down under a hollow rock far from the deathless gods and mortal men. There, then, did the gods appoint her a glorious house to dwell in: and she keeps guard in Arima beneath the earth, grim Echidna, a nymph who dies not nor grows old all her days.''

Echidna was usually considered an offspring of Tartarus and Gaia, or of Ceto and Phorcys (according to Hesiod) or of Chrysaor and the naiad Callirhoe, or Peiras and Styx (according to Pausanias, who did not know who Peiras was aside from her father). Echidna was a dracaenae, with the face and torso of a beautiful woman (depicted as winged in archaic vase-paintings) and the body of a serpent, sometimes having two serpent's tails. She is also sometimes described as Karl Kerenyi noted an archaic vase-painting with a pair of echidnas performing sacred rites in a vineyard, while on the opposite side of the vessel, goats were attacking the vines: thus chthonic Echidnae are presented as protectors of the vineyard.

The site of her cave Homer calls "Arima, couch of Typhon". When she and her mate attacked the Olympians, Zeus beat them back and punished Typhon by sealing him under Mount Etna. However, Zeus allowed Echidna and her children to live as a challenge to future heroes. She was an immortal and ageless nymph to Hesiod (Theogony above), but was killed where she slept by Argus Panoptes, the hundred-eyed giant.

The Lightning Thief
While Percy, Annabeth, and Grover are at the top of the arch they encounter Echidna who also has the Chimera with her. She quickly isolates Percy from his friends while he is waiting for a second empty elevator, and pits him against her monstrous son at the top of the arch. Percy barely manages to escape after being poisoned by the Chimera's snake tail and plummeting into the water below. She also seems greatly offended that the animal echidna (a spiny anteater from Australia) was named after her, and became even more furious when Percy brought it up.

Physical description
In the book Echidna is described through the Mist as an extremely fat woman with a chihuahua. The only clues that she was a monster were her reptillian tongue, the fact that she called her dog "Sonny" and the fact that she has slit eyes like a snake. She apparently wears a lot of denim clothing to cover up her scaly hide.

Trivia

 * In The Lightning Thief, the part where Percy and his friends encounter Chimera and Echidna was replaced with them fighting the Hydra at a replica of the Parthenon in Tennessee.