Eevee had three original evolution options in Pokémon Red and Blue: Vaporeon, Jolteon, and Flareon. These evolutions were created by using a Water Stone, Thunder Stone, or Fire Stone respectively.
Eevee’s unusual ability to evolve into different types made it distinctive among the first-generation Pokémon. Vaporeon becomes Water-type, Jolteon becomes Electric-type, and Flareon becomes Fire-type. The player’s choice depends on which evolutionary stone is used.
Later games added many more Eevee evolutions, including Espeon, Umbreon, Leafeon, Glaceon, Sylveon, and others introduced across subsequent generations. This is why modern players may remember a larger number than the original three.
Eevee’s name and branching evolution concept helped make it a recurring central Pokémon in games, animation, merchandise, and promotional material. Pokémon Yellow also features Eevee, but the three original stone-based evolutions remain the first set established by the series.