Which accessory let players trade and battle Pokémon between two original Game Boys?

The Game Link Cable let players trade and battle Pokémon between two original Game Boys.

Pokémon Red and Green, and later the international Red and Blue versions, supported connections between two systems. Players could trade version-exclusive Pokémon or battle one another, giving the games a social feature unusual for portable role-playing games of the period.

The cable was especially important because no single original game contained every Pokémon needed to complete the Pokédex. Trading encouraged players with different versions to cooperate rather than simply play separately.

Later Pokémon generations introduced other connection methods, including infrared features, wireless communication, and online services. Those newer technologies can make the original cable easy to forget. In the first generation, however, the physical Game Link Cable was the standard way to connect two Game Boy copies for trading and battling.