|Siblings||Nereus, Thaumas, Phorcys and Eurybia|
|Children||The Hesperides, The Gorgons, The Graeae, Thoosa, Scylla, Echidna, Ladon and all sea Monsters|
|Titans and Olympians|
Keto (Ancient Greek: Κητώ, Kētō, "sea monster") is a primordial sea goddess in Greek mythology, the daughter of Gaia and Pontus. Keto was also variously called Crataeis (Κράταιις, Krataiis, from κραταιίς "mighty") and Trienus (Τρίενος, Trienos, from τρίενος "within three years"), and was occasionally conflated by scholars with the goddess Hecate (for whom Trienus and Crataeis are also epithets). As a mythological figure, she is most notable for bearing by Phorcys a host of monstrous children, collectively known as the Phorcydes. The asteroid 65489 Ceto was named after her, and its satellite after Phorcys.
This goddess should not be confused with the minor Oceanid also named Keto — who appears in Hesiod's Theogony as a separate character from Keto the daughter of Pontus and Gaia — or with various mythological beings referred to as ketos (plural ketea); this is a general term for "sea monster" in Ancient Greek.
Keto in ancient texts 
Hesiod's Theogony lists the children of Phorcys and Keto as Echidna, The Gorgons (Euryale, Stheno, and the infamous Medusa), The Graeae (Deino, Enyo, Pemphredo, and sometimes Perso), and Ladon, also called the Drakon Hesperios ("Hesperian Dragon", or dragon of the Hesperides). These children tend to be consistent across sources, though Ladon is sometimes cited as a child of Echidna by Typhon and therefore Phorcys and Keto's grandson.
The Bibliotheca and Homer refer to Scylla as the daughter of Crataeis, with the Bibliotheca specifying that she is also Phorcys' daughter. The Bibliotheca also refers to Scylla as the daughter of Trienus, implying that Crataeis and Trienus are the same entity. Apollonius cites Scylla as the daughter of Phorcys and a conflated Crataeis-Hecate. Stesichorus refers to Scylla as a daughter of Phorcys and Lamia (potentially translated as "the shark" and referring to Ceto rather than to the mythological Libyan Queen).
The Scholiast on Apollonius Rhodius cites Phorcys and Ceto as the parents of the Hesperides, but this assertion is not repeated in other ancient sources.
Keto in Popular Culture 
Pliny mentions worship of "storied Keto" at Joppa (now Jaffa), in a single reference, immediately after his mention of Andromeda, whom Perseus rescued from a sea-monster. S. Safrai and M. Stern suggest the possibility that someone at Joppa established a cult of the monster under the name Ceto. As an alternative explanation, they posit that Pliny or his source misread the name as cetus - or the Syrian goddess Derceto.
Keto also appears in Rick Riordan's "Mark of Athena", where her name is spelled Keto. There, she and her husband Phorcys own an aquarium at the back of a mortal aquarium in Atlanta, Georgia, and exhibits different kinds of mythological sea creatures. Percy Jackson, Frank Zhang and Coach Gleeson Hedge gets attacked there by Phorcys, so Coach Hedge kanfu kicked Keto in the head and escapes with Percy and Frank. This angered Keto, so she sent a giant scolopendra to attack the Argo 2, but they beat it in the end. The Mark of Athena does not show anymore appearances of Keto.
- "κῆτος" in Liddell, Henry and Robert Scott. 1996. A Greek-English Lexicon. Revised by H.S. Jones and R. McKenzie. Ninth edition, with revised supplement. Oxford: Clarendon Press.
- Colitur illic fabulosa Ceto. Pliny, Book 5, chapter 14, §69; this same paragraph will be referred to as v.14, v.69, V.xiv.69 - and v.13 (one of the chapter divisions is missing in some MSS). For Keto as a transferred name, see Rackham's Loeb translation; for emendations, see The Jewish people in the first century. Historical geography, political history, social, cultural and religious life and institutions. Ed. by S. Safrai and M. Stern in co-operation with D. Flusser and W. C. van Unnik, Vol II, p. 1081, and Oldfather's translation of Pliny (Derceto).