Sadako Yamamura , reimagined as Park Eun-seo (Korean: 박은서) and Samara Morgan for their respective adaptations, is the main antagonist of Koji Suzuki's Ring novel series and the film franchise of the same name. Sadako's fictional history alternates between continuities, but all depict her as the vengeful ghost of a psychic who was murdered and thrown into a well. As a ghost, she uses nensha, her most distinctive power and weapon, to create a cursed video tape. Whoever watches the tape will die exactly one week later unless the tape is copied and shown to another person, who must then repeat the same process.

Ring 0: Birthday is the 2000 Japanese horror prequel of Ring directed by Norio Tsuruta. The film is based on a screenplay by Hiroshi Takahashi, which in turn is based on the short story "Lemon Heart" from the Birthday anthology by Koji Suzuki. Ring 0: Birthday was nominated for the 2001 edition of Fantasporto, but lost to Amores perros.