Zippo is first seen as a Charmander in the episode A Friend in Deed. It was the first of Ritchie's Pokémon to be revealed. It later battled against Ash's Charizard but was quickly withdrawn by Ritchie, this counted as a loss. That didn't matter though, as Ritchie sent out his Pikachu, Sparky, against Charizard next and Charizard refused to fight it, costing Ash the entire match.
Ash and Ritchie met again in the Whirl Islands, by this time Zippo had evolved from a Charmander into a Charmeleon. Unlike Ash's Charizard though, Zippo was still loyal and obedient towards Ritchie.
In the manga version of the battle between Ash and Ritchie at the Indigo Plateau, Zippo was a Charizard, not a Charmander like it was in the anime. In the english version of this manga the Charizard is named Charley rather than Zippo, while in the original Japanese version it is still named Zippo.