He aimlessly wandered around the Unova region when his Pokémon partner passed away. He also had a child at one point, who produced a grandchild: Benga.
In the games
Alder is first met by the Player outside Nimbasa City when he catches sight of Elesa. After Cheren says he seeks to become Champion to gain strength, Alder decides to have him and the Player have a Pokemon battle with two Preschoolers to show him their battle styles. After which, Alder is surprised his words have not swayed Cheren's heart and proceeds to enjoy the rest of the festival he is attending. Much later, after N gains control of Reshiram/Zekrom, Alder appears and N informs him about his plans to change the world along with a reminder why he is traveling around the Unova region. Following N's tip on where to find the Dark stone/Light Stone, Alder meets up with the Player in the Relic Castle, only to encounter Ghetsis. Sadly, the stone is not in the ruins and there is little time until N reaches the Pokemon league and earns the right to challenge Alder. However, to brighten things up, Lenora calls and reveals that the stone in the museum is actually the Dark Stone/Light Stone that holds the essence of Zekrom/Reshiram. Having faith in the Player being the second Hero, Alder leaves the Stone in the Player's hands and returns to the Pokemon Leauge to face N. However, Alder loses to N as his heart has not yet healed from the loss of his Pokemon. After Team Plasma's castle engulfs the Pokemon League, Alder lets the Player go in his place to face N and stop him from separating Pokemon from humans. After N's defeat, Alder arrives with Cheren and takes Ghetsis away to be arrested. However, the Shadow Triad manage to free Ghetsis, where he goes into hiding.
Alder was mentioned by Trip in BW034. He was shown to have a Bouffalant and to battle a trainer's Herdier. Alder is the one who inspired Trip to become a trainer. He appeared battling Ash in person in BW054. He has been shown to be quite forgetful, not remembering Trip or Ash's names despite being told repeatedly, even needing to be reminded where he left off on advice. Oddly, he seems to fall asleep standing up.
In Trip's flashback in BW034, it battled a unknown trainer's Herdier and defeated it with Head Smash. He reappeared in BW054, where he battled Ash's Pikachu, though he didn't really do any battling because Alder had fallen asleep and hadn't given any commands. When he woke up, he ordered Bouffalant to use Head Smash, though instead of attacking Pikachu, he attacked Alder.
Alder could also be the strongest champion yet, considering five of his Pokémon all level 75, and one is level 77.
This is debatable as Cynthia has a much better and well rounded team when you battle her in Undella town, but you also face Alder after beating the Elite Four. However Red still has the title of the strongest NPC trainer in the games with a level 80 being his weakest Pokémon in HeartGold and SoulSilver, whilst his weakest in the original Gold and Silver was still at least equal to Alder's.
In the anime, Alder did not act much like a champion, even falling asleep in the middle of a battle with Ash, which implies that he might not be as powerful as his reputation claims.
His necklace resembles Admin Dakim's from Pokémon Colesseum.
He resembles a Native American chief and his hair resembles that of Volcarona's wings.
Alder is the first Champion that is not battled the first time you defeat the Elite Four. Instead, you battle N and Ghetsis.
Alder began to wonder aimlessly throughout the Unova region after the death of one of his beloved Pokémon. It is not known what Pokèmon it was, but the only information he gives is that it was his partner, meaning that it could have been one of the three Unova Starter Pokémon.
According to Ghetsis, Alder didn't win the place of Champion, but the Elite Four asked for him to take the title.
Alder may not know how to use the PC-system, since he carries six Poké Balls around his neck and an extra three Poké Balls on his belt. Or, he just prefers to have them all with him at all times.