From Bulbapedia, the community-driven Pokémon encyclopedia.
The Elite Four (Japanese: 四天王 Shitennō, lit. Four Heavenly Kings or Big Four) are four Pokémon Trainers who are regarded as the toughest in their regional Pokémon League, short of League Champion. Those who challenge the Elite Four must have achieved all eight Badges from that region and face all four of them and the current Champion consecutively without losing to either of them. One group resides on Indigo Plateau in Kanto, and are considered the best trainers in both Kanto and Johto; another is in Ever Grande City in Hoenn; and the last known one is in the unamed Pokémon League in Sinnoh.
Kanto/Johto Elite Four
Generation I/Generation III
In the Generation I games Pokémon Red, Blue and Yellow, and the Generation III remakes, the Elite Four at the Indigo Plateau consists of:
In Generation II, the Elite Four at the Indigo Plateau consists of:
Hoenn Elite Four
In Generation III, the Elite Four in Ever Grande City consists of:
Sinnoh Elite Four
In Generation IV, the Elite Four in Foento City consists of: