The complete Pokemon RBY pokedex, part 13

Pokémon Name: Jolteon
Type: Electric
Classification: Lightning Pokemon
Pokédex Number: 135
Ability: Volt Absorb
Dream World ability: Quick Feet
Useful Attacks: Thunder
Location Found:
D/P/P/HG/SS: Evolve from Eevee
B/W: Poke Transfer, Dream World (event only)

The Electric-type evolution of Eevee focuses on, obviously, Electric-type moves, but also takes a few lessons from Fighting, Psychic and Ground types as well.

Evolution: From Eevee via Thunderstone