Eevee was classified as a Normal-type Pokémon in the original games.
Eevee first appeared in Pokémon Red and Blue as the Evolution Pokémon. Its unstable genetic code allows it to evolve into different forms depending on the evolutionary method used, which became one of its defining characteristics.
The first three Eeveelutions were Vaporeon, Jolteon, and Flareon, introduced alongside Eevee in the first generation. Water, Thunder, and Fire Stones trigger those three evolutions, but Eevee itself remains Normal-type before evolving.
Players sometimes identify Eevee with the type of one of its evolutions, especially because its branching evolution system is so prominent. Later games added Espeon, Umbreon, Leafeon, Glaceon, and Sylveon, but none of those changes altered Eevee’s original classification.