After you beat all eight gym leaders, you are granted access to Victory Road which will take you to the Pokémon League of its region where the Elite Four awaits. They are much more powerful than the gym leaders but each member of the Elite Four focus on a certain type of Pokémon. So your knowledge on type matchup is put to the test.
Which Elite Four music do you like best?

Kanto: (None, they use gym leader music)

Johto: (Again they use gym leader music)

Hoenn: Ruby/Sapphire , OmegaRuby/AlphaSapphire

Sinnoh: Diamond/Pearl

Unova: Black/White

Kalos: X/Y