Naoko Akagi was Ritsuko's mother. She was the creator of the MAGI system and the former Gehirn head technician. Naoko was involved in a romantic relationship with the recently-widowed Gendo Ikari while working at Gehirn. However, after Rei I called her an "old hag" and said that Gendo himself called Naoko that frequently, she realized that he had merely been using her affections to ensure her performance for him. In a fit of rage, Naoko strangled Rei to death and then either committed suicide or was murdered by an unknown assailant. Soon afterward, Gehirn was disbanded and the organization Nerv was formed in its place. In vol. 10 of the manga, Naoko is shown to commit suicide after killing Rei I. Ritsuko witnesses both Rei's murder and Naoko's suicide.

(Source: Wikipedia)