Eevee had three evolutions when it debuted in Pokémon Red and Blue: Vaporeon, Jolteon, and Flareon. These three forms made Eevee the first Pokémon species with branched evolutions in the games.
Each original evolution used a different elemental identity. A Water Stone produced Vaporeon, a Thunder Stone produced Jolteon, and a Fire Stone produced Flareon. The choice of stone determined which evolutionary path the player received.
Eevee later gained five more evolutions across subsequent generations: Espeon, Umbreon, Leafeon, Glaceon, and Sylveon. That brought the total number of official Eeveelutions to eight for many years.
The original total is often confused with the modern total. Questions about Eevee’s debut generation refer only to the three forms available in the first-generation games, not every evolution introduced later.