Which Pokémon game first introduced a choice of male or female playable character?

Pokémon Crystal first introduced a choice of male or female playable character in the main Pokémon role-playing games.

The female protagonist is commonly known as Kris, while the male protagonist is Ethan in later official naming. Pokémon Crystal was released for the Game Boy Color as an enhanced version of Pokémon Gold and Silver. Earlier main-series games provided only a male player character.

Crystal also added animated Pokémon sprites, a larger role for the Legendary Pokémon Suicune, and the Battle Tower. These changes distinguished it from Gold and Silver even though the games share the Johto region and much of the same storyline.

Pokémon Ruby and Sapphire followed with selectable male and female protagonists, but they were not the first games to offer that choice. Pokémon Yellow also retained a single male player character, despite adding Pikachu-focused story elements.