Wally was born in Petalburg City, Hoenn. At a young age, it was discovered he had a heart condition and asthma, which led to his family sheltering him from the outside world for most of his life. He was home schooled, and kept away from all Pokémon. One day he met a Zigzagoon in his back garden, which led to Wally's wish to become a Pokémon Trainer. When he was 10, he became friends with May, after Wally's father and her father became friends. May decided to help him become a Pokémon Trainer by helping him sneak out of his house and see Pokémon.
Wally first appeared in the series when May visited him in Petalburg City. After finding out May and Brendan were going on a journey, he yearned to do so too. Because of his shy, even meek personality, he was too afraid to speak out to his parents, despite the protesting on his behalf by both May and Brendan, when they refused to allow him to leave. May and Brendan then left without Wally, much to his sadness.
He appeared later after Lexi arrived in Petalburg City and met him while he was walking by the river. He explained his situation, and Lexi headed to his home where she successfully persuaded to allow Wally to leave his home, be it only to his Uncle's house in Verdanturf Town. Lexi suggested he tries to become a Trainer while on his way to prove to his parents he is strong enough to go it alone. He then journeys to Rustboro City with Lexi, where she helps him capture his first Pokémon, a Ralts. Upon them reaching Rustboro City, they meet up with May and Brendan, where he leaves on his journey alone.
Wally reappeared when the group arrived in Mauville City, where Wally was attempting to battle against Wattson, but his uncle refused, and so Wally said he'd battle against May to prove he was strong enough. However, May won the battle, to Wally's disappointment. He then returned to Verdanturf Town with his uncle.
When the group arrived in Verdanturf Town, Wally accompanied them to watch Brendan take part in a Contest at the Contest Hall, living at his uncles. However, in the midst of the Contest, he escaped and ran away, much to the worry of his relatives. He left a note stating that he would go on his journey and prove everyone wrong.
He didn't reappear until Lexi, May and Brendan had traversed through Victory Road, in which he battled against Lexi showing off his immense new strength and team. Despite losing to her, Wally proved that he was strong and decided to head home to show his parents his growth.
It is shown that he reappeared around Petalburg City, Despite Ralts evolving twice into its final form, Gallade. He lost against Courtney, and was shown that his Key Stone was stolen by an unknown girl.
This listing is of Wally's known Pokémon:
Wally caught Ralts with the help of Lexi. With Ralts at his side, Wally wants to put his full effort into strengthening himself as a Trainer and Ralts as a Pokémon.