Sadako's cultural appearance is of a woman in a white dress with long black hair covering her face, which has evolved into a trait for other icons of horror films, such as Kayako Saeki of the Ju-On/The Grudge franchise.
In the films, as a child, Sadako split into two different girls after murdering a journalist at her mother's botched psychic demonstration; one was kind and timid, while the other was evil and psychotic. Dr. Ikuma, Sadako's step-father, speculated that the good Sadako took after her human mother, Shizuko, and the evil Sadako took after her inhuman birth father. He allowed the good Sadako twin to live a normal life, and kept the evil Sadako twin imprisoned, feeding her growth-inhibiting drugs to keep her from physically maturing. The evil Sadako's form appears to be an inspiration for her American incarnation, Samara Morgan. Her face is hardly shown in her ghostly form, only an eye appearing in Ring, but her whole face, based on a forensic expert's interpretation, appears in Ring 2. As seen in a flashback sequence in Ring 0, the malformed, drooping eye that Sadako sports as a ghost is unique to her evil side.
The good Sadako is shown to be a quiet and gentle soul, but isolated due to her psychic powers and strange presence, which ultimately led to her death at the hands of the acting troupe she joined. She was shown to be quite caring and apologetic, attempting to aid a disabled man by healing his paralyzed legs. She fell in love with Hiroshi Toyama after he repeatedly protected her from harm and became her confidant, and her eventual lover. Her evil side is shown to be mischievous, and appears to be the embodiment of Sadako's powers and negative emotions. This is the side which takes primary control of her body after her death, exacting her vengeance upon those who watch the Cursed Videotape.
Sadako is very powerful, inheriting her psychic powers from her mother, and possibly her unknown father in the films. Her most notable power is that of Nensha, an ability which allows her to telekinetically burn images onto surfaces or into a person's mind. This allows her to create the videotape while trapped in the well. Her psychic powers also allow her to manipulate DNA and viruses, creating her mutated smallpox virus in the novels. The virus also carries her DNA, allowing her to be reborn after Mai Takano and Mitsuo Ando sleep together. In Rasen, she resurrects Ryuji Takayama, and Ando's son Takanori. Sadako is also capable of manipulating her body; such as decreasing/increasing bust/thigh/hip/ass size, increasing the amount of saliva she produces, giving herself a longer tongue, or even giving herself a male genital.
After she had been trapped in a well, Sadako felt an undying hatred toward humanity of any sort. Her evil counterpart was in primary control of her body during this time, and whenever the time came, she would always be the one to kill those who watched the Cursed Tape.
However, if there’s an outside source kind enough to help, the good Sadako can sometimes emerge.
