In the main Pokémon games, the primary goal is to travel across the region and beat all eight gym leaders. Each of them focus on a certain type of Pokémon. So knowing the type matchup is the key to victory.
Which Gym Leader music do you like best?
All of them epic to me.

Kanto: Red/Blue , Gold/Silver , FireRed/LeafGreen , HeartGold/SoulSilver , Black2/White2

Johto: Gold/Silver , HeartGold/SoulSilver , Black2/White2

Hoenn: Ruby/Sapphire , Black2/White2 , OmegaRuby/AlphaSapphire

Sinnoh: Diamond/Pearl , Black2/White2

Unova: Black/White , Black2/White2

Kalos: X/Y