Sadako Yamamura is the antagonistic force of the Japanese novel The Ring, as well as its sequels and adaptations. After being left for dead at the bottom of an old well and sealed inside, her animosity and desire for revenge causes her spirit to manifest through a video tape left in a building built over the well. Those that watch the tape view a montage of strange images related to Sadako's life, and upon the video's completion, receive a phone call through which Sadako's voice tells the viewer that he or she has seven days to live. The only way for the victim to escape death is to make a copy of the video and get someone else to watch it.
If a victim fails to follow those steps, Sadako will emerge at the end of the seventh day through a television screen or other reflective surface, and kill the victim with psychic terror.
The novels, however, indicate that copying the video does not safeguard potential victims against her curse, and that she only lets one live if she still needs them to help carry her wrath.