Which Game Freak developer secretly added Mew to the original Pokémon games?

Shigeki Morimoto secretly added Mew to the original Pokémon games.

Mew was not intended to be a normal, publicly revealed Pokémon during development. Morimoto inserted it after the games were essentially complete, using a small amount of freed cartridge space. The hidden addition became an internal surprise and was not initially documented for ordinary players.

After the games launched, Satoshi Tajiri chose to reveal Mew through a Nintendo promotional event. Its hidden status helped generate rumors and speculation, adding to the excitement surrounding the games and encouraging players to keep discussing what might exist beyond the known Pokédex.

Mew is National Pokédex number 151, immediately after Mewtwo at number 150. It is classified as a Mythical Pokémon, while Mewtwo is generally treated as a Legendary Pokémon. The two names and their genetic connection are often confused, but they are separate species.