Which programmer secretly added Mew to Pokémon Red and Green?

Shigeki Morimoto secretly added Mew to Pokémon Red and Green.

Mew was an extra Pokémon hidden in the first-generation games and was not part of the publicly announced 150 Pokémon. Morimoto added it after development was effectively complete, using a small amount of freed cartridge space.

The creature began as an internal surprise rather than a planned consumer feature. Nintendo later distributed Mew through promotional events, which made the Pokémon famous among players who had heard rumors but could not normally obtain it through standard gameplay.

Mew’s hidden status also contributed to myths about glitches and secret encounters. A later-discovered glitch allowed some players to obtain Mew without an official event, but that was different from the original method by which Nintendo intended players to receive it.