Pikachu

Pikachu is an Electric-type Pokémon.

It evolves from Pichu by happiness, and evolves into Raichu when exposed to a Thunderstone.

Pikachu is popularly known as the mascot of the Pokémon franchise.

It is the version mascot of Pokémon Yellow, where it is the only starter Pokémon in that game, and has made numerous appearences on the boxes of spin-off titles.

Ash's Pikachu
Ash Ketchum has a Pikachu that he obtained from Professor Oak in Pokémon - I Choose You!, the first episode of the Pokémon anime series. It has appeared in every non-special episode and every every Pokémon movie since.Ash was given the opportunity to release Pikachu in Pikachu's Goodbye, though Pikachu chose to stay with him. This episode also featured many other wild Pikachu.

Ashachu
Ash gets turned into a Pikachu in Hocus Pokémon by a Pokémon magician named Lily. He reverts to his human form at the beginning of the next episode.

Other
At least 20 other Pikachu appeared in Pokémon Emergency! to help Ash's Pikachu defeat Team Rocket's Jessie, James, and Meowth to send them blasting off for the first time.

Another Pikachu nicknamed Puka was owned by a man named Victor on Seafoam Island in The Pi-Kahuna. This blue-eyed Pikachu had the ability to sense tidal waves approaching.

A Pikachu has also been owned by Luana's son, Travis. Luana mistook Ash for Travis when she saw Pikachu on Ash's shoulder.In Lights, Camerupt, Action, Elijah used a Pikachu in one of his movies. This Pikachu helped Minun and Plusle on their mission to rescue Princess Kirlia from the evil Exploud.

In Mewtwo Strikes Back, Mewtwo clones Ash's Pikachu. This Pikachu can be told apart from Ash's due to spikes on the black marks at the tips of its ears. It is also comparatively more aggressive than Ash's Pikachu and slurs its speech, defects possibly caused by Ash tampering with Mewtwo's cloning machine during the cloning process.

A Pikachu also had a part in Pokémon Mystery Dungeon: Team Go-Getters out of the Gate!. He was kidnapped by a Skarmory and Team Go-Getters set out to rescue him as their first mission. Pikachu provided them with some items in the battle.