Conversation so far:
Was Mewtwo in a book?
Mewtwo has appeared as a central character in several books related to the Pokémon franchise.
What was the first book Mewtwo was in?
Mewtwo Strikes Back
What was the next book Mewtwo was in?
Mewtwo Returns
Was Mewtwo a popular character?
Mewtwo is regarded as one of the series' strongest Pokémon; it was also one of the most popular pokemon for some time.
Are there any other interesting aspects about Mewtwo?
The player first learns of Mewtwo late in Pokémon Red and Blue by reading research documents left in a ruined laboratory on Cinnabar Island.
Who is Team Rocket?
Team Rocket (ロケット団 Roketto-dan, Rocket Gang) is the crime syndicate in the Kanto, Johto, and Sevii Islands regions.

Question: How did they create him
Self-contained rewrite: How did Team Rocket create Mewtwo?