Echidna

Echidna (Έχιδνα in Ancient Greek, meaning "she-viper") is the daughter of Phorcys and Keto and is considered the mother of all monsters in Greek mythology. Typhon is her husband.

History
Echidna was described by Hesiod as a female monster spawned in a cave, who mothered, with her mate Typhon, almost every major and minor horrible monster in the Greek myths. Echidna was usually considered an offspring of Tartarus and Gaea, 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, 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 (the latter being in the form of a chihuahua because of the Mist ). She quickly isolates Percy from his friends while he is waiting for a second empty elevator, as the first was full, and pits him against her monstrous son at the top of the arch. She becomes infuriated after he confuses her with the anteater species in Australia. Percy barely manages to escape after being poisoned by the Chimera's snake tail and plummeting into the water below, to the taunts of Echidna, but while in the water his injury is healed and it is unkown where Echidna went after attacking Percy on the arch.

The Last Olympian
When Hermes references thefact the Typhon is the husband of Echidna, Percy says that he "met her on the arch, not nice," referencing when he met her in The Lightning Thief he didn't take kindly to her.

Appearance
In the book Echidna is described through the Mist as an extremely fat woman in a denim dress with a fearsome chihuahua that is her son the Chimera. The only clues that she was a monster were her reptilian tongue, the fact that she called her dog "Sonny"  (which Percy thought was its name at first) and the fact that she has slitted eyes like a snake. According to Apollodorus, Echidna was a drakaina with the face and torso of a beautiful woman (sometimes winged) and the body of a serpent, sometimes having two serpent tails. It was known that she was cursed into time cycles, so she was a young girl in the morning a Maiden in the afternoon, and an old lady at night.

When she is her true form, she still has a human head, but a snake-like body. Her tongue is forked and has fangs instead of teeth. Her skin and eyes also resemble to a reptile's as her eyes are bright green and her skin is scaly.

Children

 * Cerberus
 * Chimera
 * Clazmonian sow
 * Drakon
 * Hydra
 * Ladon (some accounts)
 * Manticore (possibly)
 * Orthrus
 * Scylla (some accounts)
 * Sybaris (possibly)

Grandchildren

 * Sphinx
 * Hellhounds
 * Nemean lion

Trivia

 * Echidna and Kampê are sometimes thought to be the same monster.