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Whales, sharks, squids, and other giant sea life, but my heart always belonged to the monsters. Did you know that young sea serpents can regurgitate the flesh of their victims and keep themselves fed for up to six years on the same meal? It's true!

–Keto, in The Mark of Athena

Keto (also spelled Ceto) is an ancient marine goddess and the mother of most sea monsters.


Keto is the daughter of Pontos and Gaea. She is most notable for bearing by her husband-brother Phorcys, an old sea god: the Gorgon sisters Medusa, Euryale, and Stheno, Phorcydes the Graeae (Graiai) (known as the Gray Sisters), Echidna, and Skolopendra. Her children have been faced by many heroes in ancient texts.

Before Princess Andromeda was sacrificed to Keto, the hero Perseus killed the goddess with Medusa's Head.

In the Series

Keto and Phrocys joined Kronos to fight against the gods in the Second Titan War. However, once Kronos was defeated and his army fell, the two were banished to Atlanta, a landlocked city in Georgia. They made the best of it and opened up an exhibit in the Georgia Aquarium.

The Heroes of Olympus

The Son of Neptune

When facing Percy Jackson, Keto's daughter Euryale mentions that her mother tends to compare she and her sister Stheno unfavorably to Medusa due to their inability to turn people to stone.

The Mark of Athena

While Percy Jackson, Frank Zhang, and Gleeson Hedge are waiting outside the Georgia Aquarium to hopefully meet Phorcys for information, they all reach into their pockets to see if they have any money to pay for entry. Frank only has three denarii, which a girl quickly scoops up and says that it is the right payment for the VIP tour. While the group feels that this is most likely a trap, they follow the girl into the aquarium and find that her name tag says Kate. As Kate gives them the tour, she seems excited about the larger sea creatures and gives the group very detailed information, but is uninformed or uninterested in the smaller creatures (calling some fish in a tank the "yellow ones").

As they pass by a gift shop, Kate tells them to take anything they want. While Percy is a bit reluctant, Frank starts to take a few shirts as he hadn't packed for a long trip, a snow globe, and a Chinese finger trap. As the group go farther into the aquarium, Kate begins to reveal she knows a lot about the group, including that Hedge was a satyr. As they look at the whale sharks, Kate tells them that they should see some of her babies out in the wild. When Percy questions if she knows Phorcys, she explains that he is who they are going to see, along with some of the really big exhibits. As they enter the Death In The Deep Seas! exhibit, Kate explains that she tried to teach some of the creatures in the tanks tricks (including a pair of Nereids), but with no luck. Percy starts to feel uneasy as Kate casually talks about sedating some of the sea creatures, even two Telekhines. Percy becomes really nervous however when Kate shows that she already knows he is a son of Poseidon. When Percy asks her what the name "Kate" stands for on her name tag, she is momentarily confused and reveals her name is actually Keto and the name tag is a misprint. When Phorcys enters the room, Keto informs him about the misprint, as his name was changed to Porky. Phorcys criticizes her for a moment, telling her that entertainment is more important than education. Coach Hedge however wants to hear more and Keto takes him down a hallway to show him a few more creatures, leaving Frank and Percy with Phorcys.

After Phorcys captured the two demigods in one of his special tanks, Keto walked past the glass with Coach Hedge. They manage to alert Gleeson that they are trapped, resulting in the satyr kicking Keto in the back of her head, knocking her out. Gleeson then helped free Frank and Percy before escaping. Keto was so angered by this, that she sent Skolopendra after the group.


Oh, those are the yellow ones.


Keto has a somewhat bubbly personality and is fond of large sea creatures. She enjoys sharing her knowledge with anyone that will listen to it and has a habit of bouncing around on the balls of her feet, as if having problems containing her energy.

Despite being the mother of sea monsters, Keto seems to be unfeeling toward of forms of life, casually talking about sedating other sea animals on display and trying to teach them tricks. She is somewhat vengeful, sending her son after the crew of the Argo II after they defeated her.


Keto appears at first as a worker for the aquarium, appearing to be in her twenties. She has frizzy black hair, which she pulls to the side in pigtails. She has dimpled cheeks, braces, and thick-framed glasses, which makes Percy think she looks like a schoolgirl nerd.

Keto wears a Georgia Aquarium polo shirt with dark slacks and black sneakers.


When speculating the identity of the "bane of Olympus", Chiron mentions Keto to be a potential candidate alongside Typhon.

  • Sea Monsters Lordship: As the Goddess of Sea Monsters, Keto has absolute control and divine authority over sea monsters. She had deep knowledge about large monstrous creatures, but has little knowledge of smaller sea animals.


  • Keto is often confused with the monster Cetus, who was the monster Princess Andromeda was to be sacrificed to. Since Keto refers to herself as a goddess in The Mark of Athena, it is assumed that in the Percy Jackson Universe these two beings are different entities.
  • The asteroid 65489 Ceto was named after her and it's satellite after her husband.
  • In myth, there was a Keto Trois, who was killed by Hercules.
  • ​​​In The Lightning Thief film, when Percy was asked by Chiron if he knew any other demigods, he looked at a mural with the name Perseus defeats Cetus, and thus knew the answer.
The Heroes of Olympus
Core Series: The Lost Hero | The Son of Neptune | The Mark of Athena | The House of Hades | The Blood of Olympus
Main Characters: Jason Grace | Piper McLean | Leo Valdez | Percy Jackson | Frank Zhang | Hazel Levesque | Annabeth Chase | Iapetus/Bob | Reyna Ramírez-Arellano | Nico di Angelo | Gleeson Hedge
Secondary Characters: Hylla Ramírez-Arellano | Dakota | Tyson | Ella | Octavian | Halcyon Green | Dr. Howard Claymore | Alabaster C. Torrington | Lamia
Minor Characters: Rachel Elizabeth Dare | Grover Underwood | Thalia Grace | Clarisse La Rue | Fleecy | Mrs. O'Leary | Kinzie | Arion | Calypso | Lou Ellen Blackstone | Chiron | Will Solace | Tristan McLean | Don | Julia | Jacob | Michael Varus | Burly Black | Medea | Midas | Lityerses | Phineas | Otrera | Echo | Narcissus | Sciron | Pasiphaë
Olympian Gods: Zeus | Hera | Poseidon | Hades | Ares | Demeter | Athena | Apollo | Artemis | Hephaestus | Aphrodite | Hermes | Dionysus
Minor Gods: Achelous | Aeolus | Asclepius | Boreas | Eurus | Hecate | Iris | Hypnos | Keto | Khione | Kymopoleia | Mithras | Nemesis | Nike | Notus | Phorcys | Serapis | Thanatos | Triptolemus | Zephyros
Roman Gods: Jupiter | Juno | Neptune | Pluto | Mars | Minerva | Ceres | Lupa | Bellona | Fortuna | Janus | Terminus | Vulcan | Mercury | Apollo (Roman) | Diana | Venus | Bacchus | Pomona | Aquilon | Hercules | Cupid | Auster | Favonius | Letus | Victoria
Giants: Enceladus | Porphyrion | Alcyoneus | Polybotes | Ephialtes | Otis | Damasen | Clytius | Mimas | Orion | Hippolytos | Thoon | Periboia
Undead: Gray | Zombie
Primordial Gods: Gaea | Tartarus | Ourae | Nyx | Chaos | Ouranos | Akhlys | Hemera | Elpis | Spes
Monsters and Magical Creatures: Cynocephali | Gorgon | Gryphon | Harpy | Basilisk | Lycanthrope | Gegeines | Cyclops | Katobleps | Unicorn | Giant Eagle | Ichthyocentaur | Satyr/Faun | Storm Spirit | Laistrygonian Giant | Lares
Related Content: Rick Riordan | Haley Riordan | Percy Jackson and the Olympians | Percy Jackson and the Olympians: The Ultimate Guide | The Demigod Files | The Demigod Diaries | The Son of Sobek | The Singer of Apollo | The Staff of Serapis | Percy Jackson's Greek Gods | Percy Jackson's Greek Heroes | The Crown of Ptolemy | Demigods & Magicians | Demigods of Olympus | Percy Jackson Demigod Collection