Mew was the hidden Pokémon added late to the original Pokémon games.
Mew was assigned National Pokédex number 151 and was not intended to be part of the ordinary player experience. Programmer Shigeki Morimoto inserted it after the game’s final debugging work, using a small amount of space freed when development data was removed.
Nintendo did not initially reveal Mew to players. Its hidden status encouraged rumors, speculation, and experimentation, and the Pokémon later became available through official promotional events. Mew’s rarity helped make it one of the most famous Mythical Pokémon.
Mew is often confused with Mewtwo because their names and origins are connected. Mewtwo is number 150 and was created through scientific experimentation based on Mew’s genetic material, while Mew is the naturally occurring ancestor-like Pokémon numbered 151.