Pikachu

Pikachu is a Pokémon companion of Ash. As the first Pokémon Ash received, he has traveled with him since the beginning and is perhaps his closest friend.

An independent Pikachu has also appeared in Pokémon Generations Abridged.

Characteristics
Pikachu, like others in his species, is a yellow mouse-like Pokémon that has an electric nature. This electricity can be controlled to a good degree, but it must be charged up beforehand and can be unleashed without warning if a proper stimulant is present.

He is generally friendly, and for the most part gets along well with Ash and his friends. That said, he's not afraid to think independently and will often give his opinion on a matter at hand.