Pikachu is National Pokédex number 25.
The Electric-type Pokémon is characterized by its yellow body, pointed ears, red cheek pouches, and lightning-shaped tail. In the original games, Pikachu could be found in Viridian Forest and the Power Plant, although it was uncommon in some locations.
Pikachu became the franchise mascot largely through its central role in the animated series. Ash Ketchum’s Pikachu was chosen as his partner because the producers wanted a Pokémon that could appeal broadly to viewers and remain outside its Poké Ball.
Pikachu is often confused with Raichu, its evolutionary successor. The two are separate species: Pikachu evolves into Raichu when exposed to a Thunder Stone in the original games. That evolution does not change Pikachu’s National Pokédex number, which remains 025.