Bulbasaur is National Pokédex number 001 in the original 151-species Pokémon Pokédex.
Bulbasaur is a dual Grass and Poison-type Pokémon introduced in the first-generation games. Its Pokédex number places it before Ivysaur and Venusaur, its two evolutionary stages. The number is a species identifier, not a measure of strength or release popularity.
Bulbasaur was one of the three starter choices offered at the beginning of Pokémon Red, Green, Blue, and their later international equivalents. The other two original starters were Charmander and Squirtle, which is a common source of mix-ups when recalling the first Pokédex entries.
The original Pokédex ends at 151 with Mew. Later generations expanded the National Pokédex with hundreds of additional species, but the sequence from Bulbasaur through Mew remains the foundational list associated with Pokémon’s first 30 years.