The original National Pokédex contained 151 Pokémon species in the first-generation games.
These species debuted in the 1996 Japanese versions of Pokémon Red and Green and the later Red, Blue, and Yellow releases. Bulbasaur is National Pokédex number 001, while Mew is number 151. Completing the collection required catching, evolving, and trading Pokémon between game versions.
The number 151 includes Mew, even though Mew was not normally obtainable through regular gameplay in the original games. Its secret status helped create early excitement around rumors, events, and special distributions.
Players sometimes confuse the original total with 150, because Mewtwo is number 150 and Mew was treated as a hidden mythical Pokémon. The second generation later expanded the Pokédex to 251 by adding 100 new species in Pokémon Gold and Silver.