While not Ash's persay, Larvitar was in an egg that Ash was given to take to Professor Elm, however in transit of the Egg it hatched into Larvitar. Like any Pokémon just hatched it had the personality of a child, but a tortured child through memories of what happened to its mother. It froze up whenever anyone other than Ash spoke to it or held it, which it eventually managed to get over. Not long after meeting, Ash managed to return it to its mother and stopped the Poachers from ever disturbing them again
Hatched from Egg and given by Elm in episode: Hatch Me If You Can!
Given back to Larvitar's Mother in episode: Mother Of All Battles! ~ Serebii
Larvitar was Ash's unofficial seventh Pokémon. This is not unusual, however, as the anime doesn't necessarily follow the rules of the games, such as Pikachu at times knowing five attacks (this was later fixed). I believe his Snorlax also knew five moves during one of the Pokémon Leagues, but I don't remember exactly.
