The Ocean Entity is a mysterious, supernatural being that resides in the sea and is the hypothetical father of Sadako Yamamura and Samara Morgan in the Ring series, the japanese and american versions respectively.
Its existence is questionable, if not entirely speculative. In the original film series, the possibility that Sadako's father is a kind of oceanic deity is arised by Heihachiro Ikuma who claimed that, athough they have sexual intercourse before, Shizuko Yamamura only got pregnant after she spent time in a beach, and given by her supernatural powers, her "true" father is everything but human. However, Shizuko have also display psychic powers of her own, meaning that Sadako might simply inherit such powers.
In the American version, however, the possibility that Samara Morgan is the daughter of a supernatural being is more solid than the japanese version, given that Samara's mother, Evelyn, claimed that her father is a sea demon, and her biological father was never found. Athough Evelyn is mentaly instable, she displays no paranormal powers of her own, leaving ambigous the origin of Samara's powers. A more obvious evidence that Samara might be the child of a sea-dealing supernatural being is her affinity and control over water, in spite of her aquaphobia.
Even so, the possibility where the Ocean Entity serves as Samara's father has been proven to be false with Galen Burke revealed to be Samara's biological father. Even so, since Galen Burke and Evelyn Bordon are normal humans, how Samara got her powers may result in the Ocean Entity having incarnated itself within Samara.