The original Pokémon generation introduced 151 species.
These Pokémon appeared in the 1996 Game Boy games Pokémon Red, Green, and Blue, with their official numbering running from Bulbasaur at National Pokédex number 001 to Mew at number 151. The total became the foundation for the franchise’s earliest slogan about collecting every Pokémon.
The number can cause confusion because the original Japanese releases were split across Red and Green, while international versions were called Red and Blue. The version names changed, but the generation’s total remained 151. Players also needed to trade between versions because some species were exclusive to one cartridge.
Mew was especially unusual: it was numbered 151, yet it was not normally obtainable through standard gameplay in the original releases. Its hidden presence helped fuel rumors and interest. Generation I later received Pokémon Yellow, but Yellow did not add a new species to the generation’s total.