The original Pokémon Red and Blue games featured 151 Pokémon species.
These species form what is now called Generation I. Their Pokédex numbers run from Bulbasaur at No. 001 through Mew at No. 151. The games were designed so that players could not obtain every species in a single version, making trading between Red and Blue an important part of completing the Pokédex.
The number 151 includes Mew, although Mew was not normally obtainable through standard gameplay in the original releases. Some Pokémon were version-exclusive, and others required trading or evolution through trading. This meant the practical challenge was broader than simply defeating opponents and finishing the story.
The original Japanese games were Pocket Monsters Red and Green, while the international releases were Pokémon Red and Blue. Later generations added many more species, but the original 151 remain especially associated with the franchise’s 1996 debut and its 30th anniversary.