What was the original development codename for Pokémon?

The original development codename for Pokémon was Capsule Monsters.

Satoshi Tajiri initially imagined a game in which creatures could be stored and released from capsules. The idea reflected influences including Japanese monster media, capsule toys, and the Game Boy’s ability to connect players through a Link Cable.

The name was later shortened informally to Capumon. Because “Capsule Monsters” could not be trademarked, the project was renamed Pocket Monsters, which was eventually romanized internationally as Pokémon.

The final concept retained the capsule idea through Poké Balls, the devices used to catch and carry Pokémon. The name change happened during a long development process that began around the early 1990s and ended with Pocket Monsters Red and Green launching in Japan in 1996.