Which Game Freak programmer created the Pokémon Mew?

Game Freak programmer Shigeki Morimoto created the Pokémon Mew.

Morimoto worked as a programmer and monster designer on Pokémon Red and Green. He added Mew late in development, when the game’s available space had been freed after unnecessary debugging data was removed. Because Mew was not part of the ordinary published Pokédex path, its existence was initially unknown to most players and even to some people involved with the game.

Mew became National Pokédex number 151, after the 150 Pokémon obtainable through the main first-generation game structure. Its hidden status helped generate rumors, magazine speculation, and player interest. Nintendo later distributed Mew through official promotional events, making it possible to obtain legitimately without relying on glitches.

Mew is often credited generally to Satoshi Tajiri because he created Pokémon, but the specific creature was designed and inserted by Morimoto. That distinction makes Morimoto the most precise answer when the question asks who created Mew itself.