From the Pokémon Wiki, a database for the Pokémon series that anyone can contribute to
The Elite Four is a title given to four trainers that qualify as being the best trainers in their respective region(s), with only the Champion above their skill level. There are currently 4 sets of Elite Four members, corresponding to the number of Generations that the main series games have been through.
In order challenge the Elite Four, a trainer must first acquire a total of 8 Badges. Upon battling them, the challenger must face all of them consecutively. Once defeated, a trainer can battle the regional Pokémon Champion for their title.
[edit] List of Elite Four Members
[edit] Kanto/Johto
[edit] Gen. I and remakes
[edit] Gen. II
[edit] Sinnoh