After countless complaints that the traditional Pokémon Championship system was way too easy, the Pokémon League came up with an effective solution that raised the difficulty and stakes of the gym system. They selected 1 male gym leader from each region, and fattened them into hairy blobs. If a trainer were to fight these enlarged Gym Leaders and lose, both them and their Pokémon are eaten.
Chuck was the trainer chosen from the Johto region to undergo this process due to his status as Johto's heaviest gym leader. Chuck agreed in a heartbeat, eager to gain more girth. Johto trainers are warned about the naked blob in the Cianwood City gym that will gladly welcome them into his massive gut.