The franchise's first generation introduced 151 Pokémon.
These original species appeared in the 1996 Game Boy games Pocket Monsters Red, Green, and Blue. They are numbered from Bulbasaur at National Pokédex number 001 to Mew at number 151.
The number is often remembered as 150 because Mew was hidden and was not normally obtainable through ordinary gameplay. Mew was later distributed through special events, and its existence became a famous source of rumors among early players.
The first-generation roster includes the three starter Pokémon, Pikachu, the legendary bird trio, and the original evolution families. Later games added new generations, but the original 151 remain the core set associated with the franchise's first release and its 30-year history.