The first generation of Pokémon games introduced 151 species.
These original species run from Bulbasaur, National Pokédex number 001, to Mew, number 151. They appeared in the 1996 Game Boy games Pokémon Red, Green, and Blue, with Pokémon Yellow later expanding the first generation’s presentation.
The number 151 is often confused with 150 because Mew was secret and was not normally obtainable through ordinary gameplay in the original releases. Mew was nevertheless part of the original Pokédex numbering and is counted as the 151st Pokémon.
The first-generation roster established many of the franchise’s most recognizable creatures, including Pikachu, Charizard, Jigglypuff, and Mewtwo. Later generations added new species, while regional forms and alternate forms made simple species counts more complicated in newer games.