Mew was the hidden Pokémon added to the original Pokémon Red and Green games.
Mew is a Mythical Pokémon that occupies National Pokédex number 151, after the 150 Pokémon that were more directly built into the original collection. Game Freak programmer Shigeki Morimoto added Mew near the end of development, after debugging had freed a small amount of cartridge space.
Nintendo did not initially publicize Mew as part of the regular game content. Most players could not obtain it through ordinary gameplay, which fueled rumors and made it a major topic among early fans. Official distributions and special events later provided legitimate ways to receive Mew.
Mew is distinct from Mewtwo, which is number 150 and appears as a major legendary Pokémon in the games and first animated film. Mew’s hidden status helped renew interest in trading, rumors, and Pokémon collecting.