Wallace
Anime
Wallace shows up in Sinnoh as a Contest Master, first appearing in "Our Cup Runneth Over!" He catches Ash's eye after watching him and Dawn spar, encouraging Ash to enter the Wallace Cup with his Buizel. He demonstrates what he's talking about with a showcase appeal using his own Milotic. He goes on to judge the Wallace Cup across several episodes, including "Staging a Heroes Welcome," "Pruning a Passel of Pals!," and "Strategy With a Smile!" He presents Dawn with the Aqua Ribbon after her victory.
The show mentions his past: he was once the Gym Leader of Sootopolis City and eventually became Champion of the Hoenn League. A later episode reveals that stylist Lila designed his Contest outfit.
Pokémon Adventures Manga
In the manga, Wallace serves as Sootopolis Gym Leader and protector of the Cave of Origin while also working as a contest master. He mentors Ruby similarly to how Winona mentored Sapphire.
Though he initially sided with Team Aqua, Wallace's strong moral compass made him the first aligned Gym Leader to break ranks—and he convinced Winona to abandon Team Magma alongside him. Eventually revealed to be the reigning Hoenn Champion in the Hall of Fame, Wallace voluntarily gave up the title, claiming he wanted to follow his mentor Juan's example by becoming a Gym Leader. Steven later confides that there's a second, unspoken reason: Wallace wanted to stay close to Winona, the Fortree Gym Leader.
Wallace and Winona shared history that fans widely interpret as romantic. While it's unclear if her feelings persist, his are pretty obvious, especially in their emotional goodbye before facing Kyogre and Groudon. When Steven's premonition suggests he won't survive that battle, Wallace reclaims the Champion title.
Other Details
He travels in an "Air Car" capable of moving across land and sky. Notably, he's the only Hoenn Gym Leader who gives nicknames to his Pokémon.
Content compiled by AnimeList.moe from publicly available sources.