As a Cyndaquil, similar to Ash's Charizard, Infernape, and Tepig, Quilava was forced to deal with an abusive trainer before Ash caught it, although unlike Charizard and Infernape it did not actually belong to that trainer.
At first, Cyndaquil had difficulty using its Fire type moves but eventually mastered Flamethrower and was capable of using it with such power that Jasmine's Steelix was roasted within its own Sandstorm.
Cyndaquil was used frequently in the Johto region and was left at Professor Oaks lab when Ash went to Hoenn.
While training for the Sinnoh League, Ash brought Cyndaquil with many of his other Pokémon. However, Team Rocket tried to cause problems and Cyndaquil evolved into Quilava.