In the original Black and White, he is wandering around Sinnoh, occasionally meeting up with the player. He is first met on Route 5 after defeating Elesa where he discusses with Cheren about his ambitions as a Trainer, which is that Cheren aims to become the champion of Unova. Alder also makes appearances throughout the journey to help put a stop to Team Plasma's plans.
Uniquely for a Champion, Alder cannot be battled the first time the player challenges the Pokémon League. By the time defeats the Elite Four, N has already defeated Alder so, the player must fight N instead, in a battle of beliefs over the fate of Unova.
In Pokémon Black and White 2, Iris has taken over in the position. Alder assists at various points in this game too, but he is based in Floccesy Town. After defeating Iris, the player can fight Alder. Upon winning, the player is given access to Black Tower or White Treehollow, depending on the game. Alder's grandson, Benga, can be fought there.