Don George first showed up in "Battle Club! A Mysterious Pokémon Appears!!" as the guy running the Battle Club. He's the one who got Ash and Iris interested in battling when they arrived, offering to set them up with an opponent. He ended up judging their match, though things got weird fast when alarms started blaring—turns out Team Rocket had caused some chaos, and security footage showed them letting loose what everyone assumed was an Umbreon.
Don George and his crew chased down the mystery Pokémon, cornering it only to discover it was just a Meowth. Meanwhile, back at the club, Ash found the actual troublemaker: a Pokabu that had gotten loose and was tearing things up. The Pokabu's previous trainer had abandoned it with a rope, which Ash used to show the Pokémon it could be cared for. Don George eventually gave Ash the green light to catch it.
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