According to Tsunekazu Ishihara, the president of The Pokémon Company, Nintendo of America didn’t like the original Japanese designs for Pokémon as they thought they looked “too cute”, so they made their own redesigns.

In particular, Pikachu was apparently redesigned to resemble a tiger with big breasts. When Ishihara asked how it was meant to be Pikachu, the American designers responded that because it has Pikachu’s tail, then that makes it Pikachu.