O-Ren Ishii was a member of the Deadly Viper Assassination Squad known by her code-name Cottonmouth. She was born on an American military base in Tokyo, Japan.
She is a half Chinese-Japanese American who was the daughter of a military man and a housewife. O-Ren eventually became the leader of a crime organization in Tokyo, where she led the Crazy 88 and Gogo Yubari. After a duel in the snow, O-Ren was defeated and killed by Beatrix Kiddo.