Unlike other pokemons, Eevee can be evolved into different creatures: Flareon, Vaporeon or Jolteon. You can choose which evolution you'd like Eevee to become, by renaming her before you evolve her.
1. Sparky will evolve into Jolteon
2. Rainer will evolve into Vaporeon
3. Pyro will evolve into Flareon
There are other eeveelutions available but they are not released into Pokemon Go yet. Look at these cute creatures:
Which one is your favourite?