Sadako Yamamura (山村 貞子, Yamamura Sadako) is a fictional character and the main antagonist of Koji Suzuki's Ring novel series and its eponymous film series. Her backstory varies between continuities, but all depict her as the vengeful ghost of a young psychic who was murdered and thrown into a well. As a ghost, she is dressed in a simple white dress with long black hair hiding her face, and uses nensha, her most distinctive power, to create a cursed videotape; whoever watches the tape will be haunted by Sadako and die exactly one week later unless the tape is copied and shown to another person, who must then repeat the same process. The titular "ring" from the novels and films refers to a ring-like visual that appears on the cursed videotape, which depicts the top of the well as seen by Sadako from its bottom. Korean and American films reimagine the character as Park Eun-seo (Korean: 박은서) and Samara Morgan, respectively, with similar backgrounds and features.
Sadako has been played by several actresses in films, including Rie Inō, who premiered the role in Ring (1998) and Ring 2 (1999), Bae Doona in The Ring Virus (1999), and Daveigh Chase in the first American film (2002). Two film adaptations largely differ from her traditional depictions: Ring 0: Birthday (2000), in which she is portrayed by Yukie Nakama, follows the events leading to her death and features her as main protagonist rather than as an antagonist, while Sadako vs. Kayako (2016), in which is portrayed by Elly Nanami, is a crossover pitching her against Ju-On and The Grudge antagonist Kayako Saeki.
Sadako and her American version, Samara are both regarded as popular horror characters, notably spreading the appearance of ghosts with Yūrei-like looks of pale girls with long dark hair in popular culture.
