Wallace plays a fairly large part in the Pokemon Adventures Manga series. His first appearance is in Ruby and Sapphire arc, during volume 18. He is first seen on a computer monitor when he is unable to attend the Gym leaders emergency meeting concerning Team Magma and Team Aqua. The Gym leaders are divided depending on which team they 'support', and Wallace aligns with Team Aqua for obvious
reasons. He makes his first official appearance (in person) in a contest that Ruby had been watching. Wallace is the winner of the competition, and catches Ruby's eye. Ruby is a fan of all things beautiful, and dreams of winning many contests. He is quick to admit that, "everything about him [Wallace] is simply too beautiful". He notes that Wallace has groomed his Pokemon extremely well, and each one is stunning on stage.
Similar to his anime and game counterparts, Wallace is a kind individual who has great passion for contests and making his Pokemon beautiful. He is quick to act if someone is in need of help, and does so with great poise. Wallace takes great pride in his abilities, and much like his anime counterpart, is rather famous for them. Famous to the point that he has his own cheer squad, at least. But even with his popularity, he still takes the time to listen to what others have to say. When Ruby challenges him to a beauty competition completely out of the blue, Wallace is happy to accept. Wallace quickly wins his matchup with Ruby, and although he was initially uninterested in taking on an apprentice, Ruby eventually caught his interest (as the son of a Gym leader, and his skills with handling Pokemon), and he agreed to take him on. Ruby and Wallace start their journey together at this point.
Wallace also considers himself to be fairly responsible. He made sure to ask Ruby to stay behind on one occasion, as he expected where he was going might be dangerous. He is very dedicated to finding out what was causing the weather disturbances and (not so) natural events that were plaguing Hoenn at the time. When he discovers Slateport city has been hit with a tsunami, he is quick to call out his water Pokemon to help save the people who were trapped in the waters. Saving those people was a task that he considered to be 'crucial' even though he had wished to go after Ruby, who had left, at the time. He later joins the rescue team, and spends time rescuing people who were being affected by the catastrophic weather conditions caused by Groudon and Kyogre.
Much like his anime and game counterparts, Wallace holds the care and protection of Pokemon in high regard. Mistreatment of Pokemon is something that he does not tolerate. When Ruby directs his frustration and anger of losing towards Mimi, his Feebas, Wallace interferes angrily and yells at Ruby for his mistreatment of Mimi. He considers blaming a Pokemon for the actions of a trainer (or lack thereof) to be inexcusable, and isn't something he will tolerate. Ruby had been unknowingly neglecting many of his Pokemon, and then blaming them for his mistakes. Wallace was very hard on Ruby in this instance, but he made it clear that Ruby had been very selfish and not considerate of his Pokemon at all. Ruby is eventually able to see how wrong he had been, and changes his ways to be more considerate of his Pokemon's feelings.
Wallace and Winona have a bit of a history in the manga series, having dated before the start of the series. Wallace still very much cares for Winona, and asks her not to take on everything by herself (she is a very independent individual). He tells her that sometimes it's a good idea to rely on others when you are overwhelmed. Winona is an important person to Wallace, and turns out to be a weakness for him when facing Team Aqua as well. Though the two are no longer romantically involved, they remain on good terms with each other.
Unlike in the anime series, Wallace's battle abilities are shown in the manga. He is a fierce competitor not only as a competition trainer, but also as a Gym leader. Wallace confronts and battles Team Magma member Tabitha in an attempt to thwart their plans to control Groudon. He can think of strategic plans which leave the enemy Pokemon unable to continue battling. As it would turn out, Wallace is actually the Pokemon League Champion, but he declined the position in favor of succeeding Juan as the Gym Leader of Sootopolis City. This was also a way for Wallace to stay close to Winona, who had become a Gym Leader around the same time. Wallace must have shown great skill in order to beat the Elite Four, and the Champion Steven Stone.
Steven Stone and Wallace are also quite friendly with one another, it's likely the two are fairly close based on their interactions together. The two of them work together along with the elite four in order to contain the backlash caused by Kyogre and Groudon battling. Unfortunately, the stress of the battle and controlling the Legendary Pokemon Regirock, Regice, and Registeel proves to be too much, and Steven passes away at Wallace's side. Wallace is clearly distraught at Steven's passing. Despite this, he continues to fight to keep the backlash from Kyogre and Goudon from destroying Sootopolis. Luckily, Steven is ultimately revived by a timeslip that is created by Ruby and Celebi. But the two are on good terms, and are seen together again in the Omega Ruby/Alpha Sapphire manga special.
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