What was the first Pokémon animated film called in English?

The first Pokémon animated film was called Pokémon: The First Movie in English.

Its full English title is Pokémon: The First Movie—Mewtwo Strikes Back. The film was first released in Japan on July 18, 1998, and was directed by Kunihiko Yuyama. Its story centers on Mewtwo, a genetically engineered Pokémon who challenges ideas about identity, creation, and what makes a Pokémon unique.

The film follows Ash, Misty, Brock, and other Trainers to New Island after they receive an invitation to battle a powerful Trainer. The theatrical feature was accompanied in many releases by the short film Pikachu's Vacation.

The North American version was released in November 1999 by Warner Bros. Pictures. It should not be confused with Pokémon: Mewtwo Strikes Back—Evolution, a computer-animated remake released in 2019. The original film remains a landmark of the franchise's expansion from games and television into cinema.