The first generation (generation I) of the Pokémon franchise features the original 151 fictional species of monsters introduced to the core video game series in the 1996 Game Boy games Pocket Monsters Red and Green (known as Pokémon Red and Blue outside of Japan).

It has been suggested that Snorlax be merged into this article. (Discuss) Proposed since April 2024.

The following list details the 151 Pokémon of generation I in order of their National Pokédex number. The first Pokémon, Bulbasaur, is number 0001 and the last, Mew, is number 0151. Alternate forms that result in type changes are included for convenience. Mega evolutions and regional forms are included on the pages for the generation in which they were introduced. MissingNo., a glitch, is also on this list.

Developed by Game Freak and published by Nintendo, the Pokémon series began in Japan in 1996 with the release of the video games Pokémon Red and Blue for the Game Boy.^[1] In these games, the player assumes the role of a Pokémon Trainer whose goal is to capture and train creatures called Pokémon. Players use the creatures' special abilities to combat other Pokémon, and some can transform into stronger species through a process called evolution.^[2] A major goal in each game is to complete the Pokémon index (Pokédex), a comprehensive Pokémon encyclopedia,^[3] by capturing, evolving, and trading to obtain individuals from all Pokémon species.^[2]

The designs of each Pokémon started as pixel art sprites by the development team first, with a single color identity chosen to work within the Super Game Boy hardware limitations.^[4] With the early development team consisting of three men,^[5] character design lead Ken Sugimori brought female developers into the project feeling they would be better able to create "cute" designs.^[6] While conceived as a group effort by multiple developers at Game Freak,^[6] the finalized designs and artworks were done by Ken Sugimori. Originally tasked with drawing the characters to illustrate a planned strategy guide by Game Freak when the games released, Sugimori drew all the sprites for the game in his style to not only unify their designs visually but also modify any design elements he felt were amiss, while trying to retain the original sprite artist's unique style.^[7] While some Pokémon have been attributed to certain developers over the years, such as Atsuko Nishida for Pikachu and Motofumi Fujiwara for Eevee and its evolutions, Game Freak has avoided attributing many Pokémon to particular individuals to keep a sense of all the developers being involved in their creation.^[6][4]

The majority of Pokémon in generation I had relatively simple designs and were similar to real-life creatures including Pidgey (a pigeon), Krabby (a crab), Rattata (a rat), and Ekans (a snake). Many Pokémon in the original games served as the base for repeating concepts later in the series.^[8] Some Pokémon, such as Squirtle, Bulbasaur and Charmander were designed based off their final evolutions and working backwards. During development they ran into issues with digital cartridge space, and many Pokémon were removed. Specifically, several Pokémon that had a three-stage evolution line were instead changed to evolve only once, resulting in a planned final evolution for Pikachu called "Gorochu" being removed from the final game.^[6]

When the games were localized for English-speaking audiences as Red and Blue, Nintendo of America gave the various Pokémon species "clever and descriptive names" related to their appearance or features as a means to make them more relatable to American children. This resulted in several pop-culture references being worked into the character's names, such as Hitmonchan and Hitmonlee, who are references to martial arts actors Jackie Chan and Bruce Lee respectively.^[9] Overseen by translator Nob Ogasawara, he voiced concern over some of the choices presented, specifically "Barrierd", which was renamed to "Mr. Mime" based on its masculine appearance.^[10] Ogasawara wanted to avoid gendered names for the Pokémon species in the event genders were introduced for them in later titles, a concern proven valid with the sequel titles Pokémon Gold and Silver.^[11][12]