In the first Pokémon anime episode, “Pokémon, I Choose You!”, Pikachu becomes Ash’s first partner. Professor Oak gives Ash Pikachu after the other three traditional starter Pokémon have already been chosen by other Trainers.
The episode first aired in Japan on April 1, 1997, on TV Tokyo. Ash initially struggles to connect with Pikachu because Pikachu refuses to stay inside its Poké Ball and does not immediately obey him. Their relationship changes when Pikachu protects Ash from a flock of angry Spearow, establishing the partnership that anchors the animated series.
Pikachu was not one of the three selectable starters in the original Pokémon Red and Green games. Those choices were Bulbasaur, Charmander, and Squirtle. The anime deliberately gave Ash Pikachu so the series could feature its recognizable mascot and create a distinctive beginning for his journey.