What was the English title of the first Pokémon animated film released in Japan?

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

Its full English title is Pokémon: The First Movie—Mewtwo Strikes Back. The film was first released theatrically in Japan on July 18, 1998, under the Japanese title Pocket Monsters the Movie: Mewtwo Strikes Back. It was directed by Kunihiko Yuyama and distributed by Toho.

The story centers on Mewtwo, a genetically engineered Pokémon created from research involving Mew. Mewtwo invites Pokémon Trainers to New Island, where the encounter develops into a conflict involving cloning, identity, and the ethics of scientific experimentation.

The North American version arrived in November 1999 and included the short Pikachu's Vacation. The film is often called simply Mewtwo Strikes Back, but Pokémon: The First Movie is the canonical English title used for its international release.