Sadako Yamamura

In the original novel, Sadako was a hermaphrodite, meaning that she was both male and female. In both the novels and movies, it is hinted that she is the daughter of some oceanic based entity, making her a quasi-oceanic demigod.

Her name combines the Japanese words for "chaste" (sada) and "child" (ko).
Sadako Yamamura (山村貞子 ,Yamamura Sadako?) is the antagonist in Koji Suzuki's novel Ring and the 1998 film adaptation. She returns as the antagonist in Rasen, is the protagonist in Ring 0: Birthday, and appears in the Korean and American remakes of the Ring cycle films.
Character

Sadako's character is not directly portrayed in Ring, but is expanded briefly in Rasen and to a much greater extent in Ring 0: Birthday, although there are differences in these various portrayals.
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Most other incarnations share one thing in common - Sadako's need to reproduce, something she can not do herself, as she is portrayed as an intersexual. This is generally the reason why she creates the "Ring Virus", since she will "live on" in it, as long as her DNA (merged with that of the smallpox virus) still exists. In some incarnations where the "Ring Virus" is just treated as a mysterious phenomenon, and not a biological virus, she generally created it for the purpose of wreaking vengeance on humanity.