Beatrix Kiddo, also known as The Bride, is a character played by Uma Thurman in Quentin Tarantino's Kill Bill films. Her Deadly Viper Assassination Squad codename was Black Mamba. Not much is known of her background, except for what is shown in the film, along with a few snippets of flashback.
Kiddo goes on a brutal killing campaign in order to avenge the murder of her fiancé, friends, and others at a wedding rehearsal. Her targets consist of the other members of the Deadly Viper Assassination Squad who carried out the massacre: O-Ren Ishii, Vernita Green, Elle Driver, Budd, and Bill.
Kiddo (whose real name is not revealed until Kill Bill Volume 2) was once Bill's lover, protegé, and second-in-command; his favoritism of her earned her the jealousy and scorn of the other Vipers, especially Driver. While already a gifted practitioner of kung fu and fencing, Kiddo truly became a force to be reckoned with after undergoing harsh, demanding training at the feet of the taciturn, unforgiving martial arts sage Pai Mei; under his tutelage, she became far and away the most skilled assassin in Bill's gang. She became the first person (so far as we know) to whom Pai mei taught all he knew, including his Five Point Palm Exploding Heart Technique, in which a person kills another by jabbing five key pressure points around the heart, causing it to explode after they take five steps.
When Kiddo found out that she was pregnant with Bill's child, however, she despaired at the thought of raising a child in a world of hired killers and decided to leave him. That night, an assassin from a rival gang tried to kill her, but relented and let her go after hearing her story. Kiddo then let Bill believe that she had been killed, went into hiding in Texas under the name "Arleen Machiavelli", and got engaged to a young man named Tommy.
Bill eventually found her, however, and showed up at her wedding rehearsal. Initially promising that he would try not to interfere and even introducing himself to Tommy as her "father", Bill allowed the execution of the entire wedding party to proceed, and performed the coup de grace on the heavily pregnant Kiddo personally, shooting her in the head.
Kiddo survived, but was put into a seemingly irreversible coma. That night, Driver, disguised as a nurse, sneaked into the hospital where Kiddo lay and was about to kill her with a syringe full of poison, but Bill called off the hit at the last minute on the basis that it was not right to kill her in her sleep. She remained comatose for four years, during which an orderly named Buck repeatedly raped and prostituted her.
One day, as one of Buck's "customers" was about to violate her, she suddenly snapped out of the coma and killed them both. Believing that her child had been aborted when she had been shot, she swore revenge on the entire Deadly Viper Assassination Squad. She flew to Japan and sought out legendary swordmaker Hattori Hanzō, whom she persuaded to come out of retiurement and forge her a deadly katana (samurai) sword, even though he had sworn an oath never to make "something that kills" again many years ago. He did this becaue he was favorably inclined to her quest, having been responsible in part for Bills training himself. She then tracked down and killed Ishii and Green, hacking her way past Ishii's personal army, the so-called Crazy 88 to do so.
Budd, however, proved to be much more difficult to kill; after stunning her with a shotgun blast of rock salt and immobilizing her with an anesthetic, he buried her alive. Recalling Pai Mei's teachings, she found the weakest spot in the coffin lid, struck it until it broke, and tunneled her way back to the surface. She returned to Budd's trailer to find him dead from a Black Mamba bite, and Driver waiting to engage her in battle. After Driver revealed that she had killed Pai Mei, Kiddo ripped out her remaining eye (one had already been similarly removed by her teacher), left her in the desert to die, and went to find Bill.
When she did track him down, however, she was astonished to find that her daughter, B.B., was alive and living with her father, who doted on her. They spent a night together as a family, with Bill offering reasons for his betrayal and rejecting the idea that she could have ever been happy as anything other than a killer. Their peace made with each other, Kiddo then completed her revenge by killing Bill with the Five Point Palm Exploding Heart Technique. The same night, she took B.B. with her to raise on her own. Her present whereabouts are unknown.