Lest we forget, Ash and Charizard (whom he first acquired as a lowly Charmander) have been together almost since the beginning.
And even though Ash has gotten burned on several occasions, it’s clear that Charizard has been one of Ash’s most faithful companions on his journey to become a Pokémon Master.
When Charmander’s original trainer abandoned it for being too weak, Ash happily made it a part of his team.