Eevee had three evolutions when it first appeared in Pokémon Red and Blue: Vaporeon, Jolteon, and Flareon.
Each original Eeveelution required a different elemental Evolution Stone. A Water Stone evolved Eevee into Vaporeon, a Thunder Stone produced Jolteon, and a Fire Stone produced Flareon. This made Eevee unusual because one Pokémon could branch into several different species.
Eevee later gained five additional evolutions: Espeon, Umbreon, Leafeon, Glaceon, and Sylveon. That brought the total to eight, which is why modern players may remember eight rather than the original three.
The three earliest forms were introduced alongside Eevee in the first-generation games. Eevee was also the only species with branched evolutions in the first generation, making its design an early example of the franchise’s interest in multiple evolution paths.