Pikachu (/ˈpiːkətʃuː/ ^ⓘ; Japanese: ピカチュウ, Hepburn: Pikachū) is a Pokémon species in Nintendo and Game Freak's Pokémon media franchise, and the franchise's mascot. First introduced in the video games Pokémon Red and Blue, it was created by Atsuko Nishida at the request of lead designer Ken Sugimori, with the design finalized by Sugimori. Since Pikachu's debut, it has appeared in multiple games including Pokémon Go and the Pokémon Trading Card Game, as well as various merchandise. While Pikachu has been primarily voiced in media by Ikue Ōtani, other actors have also voiced the character including Kate Bristol, Ryan Reynolds, Kaiji Tang, Hidetoshi Nishijima, Tōru Ōkawa, and Koichi Yamadera.

Classified as an Electric-type Pokémon, Pikachu is a large yellow mouse with a lightning bolt-shaped tail, and red sacs on its cheek which can generate large amounts of electricity. Originally designed to be the first part of a three-stage evolution line in Red and Blue, Pikachu evolves into Raichu through the use of a "Thunder Stone" item, with Raichu intended to be able to evolve into 'Gorochu'. However 'Gorochu' was removed due to cartridge space concerns, and a pre-evolution for Pikachu, Pichu, was later added in the sequel titles Pokémon Gold and Silver.

Pikachu is widely considered to be the most popular and well-known Pokémon species, largely due to its appearance in the Pokémon anime television series as the companion of series protagonist Ash Ketchum. Pikachu has been well received by critics, with particular praise given for to its cute design, and it has been regarded as an icon of both the Pokémon franchise and Japanese pop culture as a whole.

Pikachu is a species of fictional creatures called Pokémon created for the Pokémon media franchise. Developed by Game Freak and published by Nintendo, the Japanese franchise began in 1996 with the video games Pokémon Red and Green for the Game Boy, which were later released in North America as Pokémon Red and Blue in 1998. In these games and their sequels, the player assumes the role of a Trainer whose goal is to capture and use the creatures' special abilities to combat other Pokémon. Some Pokémon can transform into stronger species through a process called evolution via various means, such as exposure to specific items. Each Pokémon have one or two elemental types, which define its advantages and disadvantages when battling other Pokémon. A major goal in each game is to complete the Pokédex, a comprehensive Pokémon encyclopedia, by capturing, evolving, and trading with other Trainers to obtain individuals from all Pokémon species.

Midway through Red and Blue's development, lead designer Ken Sugimori felt that the game needed more "cute" Pokémon and was struggling to conceive of such designs. Attributing it to his male perspective, he brought in female Game Freak staff including Atsuko Nishida to join the development team. Tasked with developing the Pikachu species and its evolutionary line, she was given specific guidelines to work with, namely its role as an Electric-type Pokémon, that it evolved twice, and that the final evolution should "look strong". Pikachu evolves into Raichu through use of the game's "Thunder Stone" item. Raichu was originally planned to evolve into a Pokémon species dubbed Gorochu, but this was cut due to cartridge space concerns. Later in the franchise, Sugimori would create a Pokémon that evolved into Pikachu named Pichu to complete the trinity. Nishida developed the original Pikachu sprites using a single color identity chosen to work within the Super Game Boy's hardware limitations. Afterwards, the design was finalized by Sugimori who, towards the end of development, drew the promotional art of all the species to give them a unified look and make any last-minute changes.

Standing 0.4 metres (1 ft 4 in) tall, Pikachu is a bipedal rodent with long ears and feet but short arms. It has yellow fur, long pointed ears that end in black tips, red cheek sacs, and a tail shaped after a lightning bolt. It has a black pattern on its back, as Nishida felt since this part of the character would face the player during gameplay, it "would be better to put something there rather than having it be perfectly smooth." While preliminary designs took inspiration from mice or rabbits, as the Pokémon Rattata already existed at this point in development she instead modeled the species after squirrels. Nishida stated in an interview that she was obsessed with squirrels at the time due to their "comical" movement, and had the idea to have Pikachu store electricity in their cheeks similar to how squirrels store food. Pokémon creator Satoshi Tajiri however chose to change the species to be a type of mouse when he was designing the setting.

Nishida was helped during the creation process by fellow developer Koji Nishino, who grew fond of Pikachu as a result and consistently encouraged the design to be made cuter, something she was happy to oblige. Due to his fondness for Pikachu, he made it more difficult to find in the original games, joking he wanted to "keep it for himself". Despite initial concerns that players would not be interested in seeking out Pikachu, Sugimori showed the design to the game's development team, where the character was instantly popular. Pikachu's design with the release of Red and Blue was initially pudgier in build, but in media and games that followed was changed over time to have a slimmer waist, straighter spine, and more defined face and neck. According to Sugimori, these changes originated from the anime adaptation of the franchise where it made Pikachu easier to animate, and were adopted to the games for consistency. The older design, nicknamed "Fat Pikachu" by fans of the series, was revisited in Pokémon Sword and Shield, where Pikachu received a special in-battle "Gigantamax" form resembling its original design. This Gigantamax form was designed by James Turner, who served as art director for Sword and Shield.

Series director Junichi Masuda stated that Pikachu's name was one of the most difficult to create, due to an effort of wanting to make it appealing to both Japanese and American audiences. The name is derived from a combination of two Japanese onomatopoeia: ピカ (pika), a sparkling sound, and チュー (chū), a sound a mouse makes. When localizing the games for the United States, Nintendo of America's staff initially proposed to redesign "cute" Pokémon in order to appeal to an American audience. According to Pokémon Company president Tsunekazu Ishihara, they had proposed to change Pikachu to look like "something like a tiger with huge breasts. It looked like a character from the musical Cats." Taken aback, he had asked them how it was supposed to be Pikachu, and in response they pointed to the character's tail. This suggestion was scrapped, and Pikachu used the same design in the west as it did in Japan. However, Nintendo CEO Satoru Iwata recalled the events differently. At the time, Iwata was working at HAL Laboratory, and one of the localizers upon seeing the Pokémon designs stated "Something this cute can't be called a 'monster'", arguing monsters should be muscular and fearsome. As a result, the localization team drew up a muscular redesign of Pikachu for Iwata to submit to Game Freak. Iwata refused, stating his reaction was "There's no way we can show this to the people who made Pokémon."