The first-generation Pokémon games introduced 151 species in their original Pokédex.
The count runs from Bulbasaur, listed as number 001, to Mew, listed as number 151. The original games’ main objective was partly to obtain and record these creatures, although completing the full Pokédex required trading because individual versions contained exclusive Pokémon.
The number 150 can cause confusion because Mew was a hidden Mythical Pokémon and was not normally obtainable through ordinary gameplay. Nevertheless, Mew was officially included as the 151st Pokémon in the original National Pokédex order.
Later generations added new regional groups, so the total number of Pokémon species grew far beyond the original 151. The first-generation figure remains a major anniversary fact because it describes the complete original roster rather than the number available in a single cartridge.