Pikachu was designed by Atsuko Nishida and had its final design completed by Ken Sugimori.
During Pokémon Red and Blue’s development, lead designer Sugimori wanted more cute Pokémon to balance the game’s tougher-looking creatures. Nishida was asked to create an Electric-type Pokémon that could evolve twice and would eventually become strong. Her work produced the character that became Pikachu.
Nishida’s early design drew inspiration from squirrels, including the idea of storing electricity in cheek pouches. Satoshi Tajiri later described Pikachu as a mouse Pokémon, while the final game design retained the squirrel-inspired visual ideas. Koji Nishino also influenced the character’s cuteness during development.
Pikachu’s importance grew dramatically after the anime selected it as Ash Ketchum’s partner. That role made Pikachu the franchise mascot, even though players could choose Bulbasaur, Charmander, or Squirtle as their first partner in the original games.