The Viridian Gym is a Pokémon League Gym that is controlled by Team Rocket. The Gym Leader was formerly Giovanni, but he left during an emergency and Jessie took over. The gym was then destroyed during her battle with Ash Ketchum and by the end of the Hoenn saga, Agatha filled in while a new leader was being found.
In Pokémon Emergency!, Ash Ketchum rushed here after his Pikachu had been weakened by Spearow. The Team Rocket trio then attacked the Center and Ash, Misty and Nurse Joy attempted to save the Poké Balls by transferring them to the Pewter City Pokémon Center. It was then destroyed by a combination of the ThunderShock of both Ash's Pikachu and Nurse Joy's Pikachu. By the time of The Battle of the Badge, it had been repaired. In Gotta Catch Ya Later!, the Nurse Joy had been replaced.