Pikachu has National Pokédex number 025 and became the Pokémon franchise's mascot.
Pikachu is an Electric-type Pokémon first introduced in the original Red and Green games. Its recognizable design includes yellow fur, red cheek sacs, black-tipped ears, and a lightning-bolt-shaped tail. In the games, Pikachu evolves into Raichu when exposed to a Thunder Stone.
The anime made Pikachu especially famous by pairing it with Ash Ketchum. The character was chosen because it was cute, visually distinctive, and appealing to a broad audience rather than being tied to only one of the three starter choices.
Pikachu's number is often confused with its position in a regional Pokédex or with the numbers of its evolutionary relatives. Pichu is number 172, while Raichu is number 026 in the National Pokédex.