What was Pokémon called during its earliest development?

During its earliest development, Pokémon was called Capsule Monsters.

Satoshi Tajiri conceived the project around the idea of collecting creatures and exchanging them between Game Boy systems. The Game Boy’s link cable inspired the concept because it allowed two players to connect their consoles and interact. Tajiri initially used the working title Capsule Monsters for the project.

The name later changed because Capsule Monsters could not be trademarked. The development team considered the shortened form Capumon before settling on Pocket Monsters, the Japanese name that became Pokémon internationally. Pokémon is a contraction of Pocket Monsters rather than the original development title.

The name change occurred while Game Freak was developing what became Pokémon Red and Green. This early title is easy to miss because it was never released as a commercial Pokémon game. It belongs to the franchise’s development history, before the final branding and creature designs were established.