Pikachu is the starter Pokémon given to the player in Pokémon Yellow.
Released in Japan in 1998, Pokémon Yellow is an enhanced version of the original Red and Blue games. It was designed to resemble elements of the Pokémon anime, so the player begins with Pikachu rather than choosing freely among Bulbasaur, Charmander, and Squirtle.
Pikachu also behaves differently from ordinary Pokémon in the game. It follows the player on the overworld, has a distinctive voice, and reacts to the player’s actions through a friendship-style happiness system. These features helped connect the game to Pikachu’s prominent role in the television series.
The rival’s starter is also changed: instead of receiving the type-advantaged starter from the original games, the rival begins with Eevee. Pokémon Yellow was released in Japan on September 12, 1998, then reached North America in October 1999 and Europe in June 2000.