Ash's Pikachu

In the Pokémon animé, Pikachu was Ash Ketchum's first Pokémon, given to him by Professor Oak. Though Pikachu didn't like Ash at first, Ash demonstrated his willingness to sacrifice himself for Pikachu, and they became fast friends. Pikachu, who is rather independent minded in general, believes that it is strong enough without evolving and refuses to evolve into a Raichu. Pikachu is implied to be male, but is rarely addressed with a gendered pronoun. If a Yellow version Pikachu is traded to Silver, Gold, or Crystal, that Pikachu (since Yellow version is loosely based off the anime) is always female.

Early in the series, Pikachu was given an operation to increase the strength of the electric sacs in its cheeks in order to beat the first gym leader, Brock. Despite this, Pikachu can also get a cold and go out of control when it cannot release its electricity. Most notably, exposure to a magnetic field will cause Pikachu to get a cold. This has been done to Pikachu twice in the series, both times by Team Rocket: the first time, Pikachu was cured when the extra electricity was used in attacks against a group of Grimer and Muk, and in the second time, Pikachu was inadvertently cured by one of Team Rocket's battery robots, which subsequently overloaded and exploded.

Many of the Pokémon animated shorts with all-Pokémon dialogue have featured Pikachu as the main character, and as the main voice of reason. As such, Pikachu is often a leader, helping to break up conflicts among other Pokémon.

Like many other Pokémon, Pikachu communicates only by saying syllables that are in its own name. Its most common sentence is "Pika-pika". When it wants to talk to Ash it says "Pika-pi," which sounds similar to "Satoshi", and it refers to Togepi as "Pipipi", probably because in Japanese, "pii" means "little".

The phrase "Pika-pika" is often considered funny, particularly to Japanese speakers' ears. The Japanese expression "pika-pika hikaru" means stroke of lightning; it is also used to denote a small bald spot on the very top of the head still surrounded by hair.

Pikachu is voiced by Ikue Ootani in all versions of the anime, except in early episodes of the English dubbed series, in which Rachael Lillis provided the voice in cases where another character's voice overlaps Pikachu's.