In Ruby, Sapphire and their remakes, Wallace leads the Sootopolis Gym and awards the Rain Badge; his Ruby and Sapphire team is Luvdisc, Sealeo, Seaking, Whiscash and Milotic. He is close to Steven Stone and helps him during the Cave of Origin crisis.
Emerald moves him up. He guides the player to the Sky Pillar to wake Rayquaza, hands the Gym back to his former teacher Juan, and waits at Ever Grande City as Champion in Steven's place, with Wailord, Tentacruel, Ludicolo, Whiscash, Gyarados and Milotic. In Omega Ruby and Alpha Sapphire's Delta Episode he turns out to descend from the ancient people of Sootopolis, which lets him open the Sky Pillar, and he battles the player with that Champion team before the climb.
Wallace is as famous for Contests as for battles. In Omega Ruby and Alpha Sapphire he can be met in Master Rank Beauty Contests, and his niece Lisia competes in Contests too. In the anime he is a Contest Master and former Hoenn Grand Festival winner who hosts the Wallace Cup in Sinnoh, where Dawn wins the Aqua Ribbon.
His Supporter draws three cards; your opponent may then draw one, and if they do you draw one more. Silver Tempest printed it as an Uncommon (#166) by Megumi Mizutani, a full-art Ultra Rare (#194) and a rainbow Secret Rare (#208), both by Ryuta Fuse.
The rainbow Secret Rare, numbered past the set's main run.
The full-art Ultra Rare by Ryuta Fuse.
The regular Uncommon, illustrated by Megumi Mizutani.
Both. He leads the Sootopolis Gym in Ruby, Sapphire, Omega Ruby and Alpha Sapphire, and he is the Champion in Emerald, where his mentor Juan runs the Gym instead.
Milotic, the last Pokémon of both his Gym Leader and Champion teams and his partner in Contests.
It draws three cards. Your opponent may draw a card, and if they take it, you draw one more.

CHAMPION
3 Trainer cards · 0 partner Pokémon
Wallace is Hoenn's Water-type master: Sootopolis Gym Leader in Pokémon Ruby and Sapphire, Champion in Emerald, and a Contest star with his Milotic. His Silver Tempest Supporter draws three cards and was printed as an Uncommon, a full-art Ultra Rare and a Secret Rare.
No published index yet — too few of Wallace’s cards trade often enough to strike one.