Ai Fuji

Ai, known as Amber in the English dub, is the daughter of Dr. Fuji, the creator of Mewtwo, and Mewtwo's first friend. When Mewtwo first meets her, she is a clone, and is thus referred to as Aitwo. She teaches him about the world using her memories of her first life. Her death is the first catalyst of Mewtwo's life, but she's tragically wiped from his memory.

She appeared as a speaking character during the beginning sequence that was originally cut from the English dub of Mewtwo Strikes Back, but later featured on the Mewtwo Returns DVD as The Uncut Story Of Mewtwo's Origin. She also first appeared in The Birth of Mewtwo radio drama, released in CD format exclusively in Japan.

(Source: Bulbapedia)