Android 0 is the first Android ever created. The creator himself, Dr. Gero Sr. turned into Android 0. He wanted revenge on the Saiyans, (especially Bardock) which is why more Androids were created to kill Goku. The Android was sent to Planet Vegeta to kill Bardock. He found Bardock and nearly killed him. However, Bardock killed him with the Final Spirit Cannon in the end, which also killed Dr. Gero Sr. He also has a possible second, third, fourth, fifth, and sixth form, but were never seen.