Charizard first appeared as a Charmander while Professor Oak was about to give away the starter Pokémon to Satoshi and Shigeru. Charmander attacked a Pidgey when it was going to attack Satoshi. At the lab, Satoshi immediately chose Charmander as his starter Pokémon. He tested out Charmander by battling Shigeru's Squirtle in which the Fire-type was able to defeat Squirtle despite the type-disadvantage. Charmander woke up Satoshi with its tail and Satoshi traveled with it all the way to Pewter City.
Arriving at the Pewter Gym, Charmander challenged Brock's Onix where it showed some incredible speed by dodging some of Onix's attacks and managed to defeat Onix by striking it on its rocky spine. Charmander has a battle with Team Rocket's Beedrill when they took over Miracle Cycle. It was able to easily defeat Beedrill which sent Team Rocket running. Satoshi and Charmander arrive in Cerulean Gym where Satoshi attempted to use it to battle Misty but Charmander refused to do so as it was afraid of the water since it would put out the flame on Charmander's tail.
Later, Charmander had a rematch with Shigeru's Squirtle on the S.S. Anne where once again, Charmander was able to defeat Squirtle. The battle caused Charmander to evolve into Charmeleon. Satoshi and Charmeleon head to the Vermilion Gym and battled Lt. Surge's Electabuzz. Charmeleon struggled with dealing with Electabuzz at first but finally defeated it with a combination of tying it up with a barbed-wire fence and attacking it with an unidentified Fire-type move.
Satoshi headed to Celadon City and sent out Charmeleon to battle Erika's Vileplume in the Gym there. When Vileplume's Petal Dance blinded Charmeleon, it caused a piece of flames from Charmeleon to accidentally burn part of Erika's kimono. Charmeleon attempted to put out the fire by slashing the burned areas. The referee was going to declare Erika as the winner since she saw Charmeleon attacking Erika, but Erika rewarded Satoshi the Rainbow Badge as Satoshi raised Charmeleon to be very kind.
Later, Charmeleon battled with Blaine's Arcanine. After defeating Arcanine, Charmeleon evolved into Charizard. Blaine borrowed it while he and Satoshi attempt to capture an Articuno at Seafoam Islands. With Satoshi's help and Charizard's method of flight, Blaine was able to get close enough to Articuno and catch it. Satoshi flies back home on Charizard and then flew to Viridian Gym to face the final Gym Leader.
During the Gym battle against Giovanni, Charizard was substituted for Lapras after Lapras got hit by Rhydon. When Charizard dealt damage to Rhydon, it caused Giovanni to explain to Satoshi about his character and rewarded Satoshi the Earth Badge. While flying back home, Satoshi and Charizard get attacked by Shigeru and Pidgeot. Since Charizard just finished the battle with Giovanni, Pidgeot sent it flying straight down.
Back home, Charizard once again woke up Satoshi using the same technique when it was a Charmander. They fly away to Indigo Plateau to challenge the Elite Four. Charizard battled Lance's Dragonite where it was able to defeat Dragonite with an unidentified Fire-type move. It then battled with Shigeru's Blastoise and won, earning Satoshi the title as Champion. Sometime after Charizard dodged Blastoise's unidentified Water-type move, it hit one of the pillars and Satoshi pushed Shigeru out of the way to prevent him from getting crushed.