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, as well as all large animals that live in the seas and oceans.


Keto is the daughter of Pontus and Gaea. She is most notable for bearing by her husband as well as her brother Phorcys, an old sea god, the Gorgon sisters Medusa, Euryale, and Stheno, at the same time Phorcydes the Graeae (Graiai), also known as the Gray Sisters, Echidna, and Ladon.


Keto with Pontus and a lion attacking the giants in the First Giant War from the Pergamon Zeus Altar

Not much else is known about Keto, as she herself doesn't appear much in Greek Mythology. However her children have been faced by many heroes in ancient texts. With her brother Phorcys, she gave birth to some of the most powerful sea monsters in ancient history.

In the Series

Keto and her brother joined Kronos to fight against the gods in the Second Titan War. However, once Kronos was defeated and his army fell, Keto and Phorcys 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.

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Keto's husband, Phorcys

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.


Keto has a somewhat bubbly personality. She is incredibly fond of large sea creatures, but has little knowledge of smaller animals. For example, she constantly tells people facts about the large monstrous creatures, but when Frank asked pointed to a fish and asked what type it was, she said: 

Oh, those are the yellow ones.


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, she seems to be unfeeling toward of forms of life, casually talking about sedating other sea creatures on display and trying to teach them tricks. She is also somewhat vengeful, as she sent Skolopendra 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. She wears a Georgia Aquarium polo shirt with dark slacks and black sneakers.


  • She presumably possesses the standard powers of a goddess.
  • Sea Monsters Lordship: As the goddess of sea monsters, she has absolute control and divine authority over sea monsters.


  • 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 asteroid 65489 Ceto was named after her and it's satellite after her husband.
  • Alternatively with the Keto killed by Perseus, there was also Keto Trois, killed by Hercules.
  • Like Typhon being the most powerful storm deity, Keto is considered to be the most powerful ocean monster-deity.
  • Despite being depicted as a monster in mythology, Keto refers to herself as a goddess in The Mark of Athena.
  • When speculating the identity of the "bane of Olympus", Chiron mentions Keto to be a potential candidate alongside Typhon. He additionally refers to her as a sea monster, rather than a goddess.[1]


  1. The Titan's Curse, paperback, UK edition, pg. 91
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 | 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 | Iapetus/Bob
Minor Characters: Rachel Elizabeth Dare | Grover Underwood | Thalia Grace | Fleecy | Mrs. O'Leary | Kinzie | Arion | Calypso | Lou Ellen Blackstone | Chiron | Will Solace | Tristan McLean | Don | Julia | Jacob | Michael Varus
Olympian Gods: Zeus | Hera | Poseidon | Hades | Ares | Demeter | Athena | Apollo | Artemis | Hephaestus | Aphrodite | Hermes | Dionysus
Minor Gods: Achelous | Aeolus | Asclepius | Boreas | Eurus | Enyo | 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 | Orcus
Giants: Enceladus | Porphyrion | Alcyoneus | Polybotes | Ephialtes | Otis | Damasen | Clytius | Mimas | Orion | Hippolytus | Thoon | Periboia
Undead: Medea | Midas | Lityerses | Gray | Phineas | Otrera | Echo | Narcissus | Sciron | Pasiphaë
Primordial Gods: Gaea | Tartarus | Ourae | Nyx | Chaos | Ouranos | Akhlys | Erebos | 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
Related Content: Rick Riordan | Percy Jackson and the Olympians | Demigods and Monsters | 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
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