Pokémon Red and Green took six years to complete.
Satoshi Tajiri conceived the core Pokémon idea after seeing the Game Boy and considering how its Link Cable could connect two players. He imagined creatures moving between systems, combining his interest in insect collecting with a new kind of social game interaction.
Game Freak pitched the project to Nintendo, but development was unusually lengthy and financially difficult. The team had to build a large role-playing game around collecting, training, battling, and trading creatures while also developing the connectivity features that made the concept distinctive.
The games were eventually released in Japan on February 27, 1996. Pokémon Red and Green became the foundation for the later international Red and Blue versions. The six-year development period is often overlooked because the finished games look simple by modern standards, but their systems, artwork, and link-based trading required substantial work for the Game Boy.