Torterra, while still a Turtwig, first became partners with Paul when he became a Pokémon trainer. Traveling through the Hoenn, Johto and Kanto regions, Turtwig competed in each of the region's league conferences and evolved into Torterra at some point during these adventures. However, this took place after Reggie's battle against Brandon at the Battle Pyramid. It made its first anime appearance in Top-Down Training! where it was used in a battle against Cynthia's Garchomp. Quickly launching a powerful Giga Drain attack, Torterra was initially able to bring the Land Shark Pokémon to its knees. This was followed up by a tremendous Frenzy Plant; however, Garchomp proved too powerful for Torterra and was able to withstand the attack and knock out Torterra with a single Brick Break.
It also appeared in Smells Like Team Spirit! where it was used in the semi-finals of the Hearthome City Tag Battle Competition. It was paired off with Ash's Staravia and was up against Brock's Croagunk and Holly's Farfetch'd. It defeated both its opponents single-handedly.
Torterra appeared again in Aiding the Enemy! where it saw the battle between Ash's Turtwig and Paul's Honchkrow. It also witnessed the evolution of Turtwig and its loss of speed. While Grotle was training to become faster, Torterra came forwards on its own to show it that a Pokémon could still be powerful by coping with its lack of speed with strong defense. To prove this, it battled against Ash's Gliscor in a practice match. After teaching this, Torterra returned to Paul's camp. Paul, while curious as to where Torterra had gone, did not push the issue.
It appeared again during Ash and Paul's full battle in Pedal to the Mettle!. It fought against Ash's Gliscor and Ash's Staraptor before being recalled. In Evolving Strategies!, it fought against Ash's Chimchar, where it was shown to control its Stone Edge at will to mow down its faster opponents. It then defeated Gliscor before being recalled when Ash's Pikachu was sent out.
From what's been seen of its personality, it appears to be calmer and kinder than Paul or his other Pokémon, as it actually went out of its way, against Paul's wishes, to help Ash's Grotle improve its fighting skill.
A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.
Trivia
This is the second time one of Ash's rivals have had an evolved form of a starter Pokémon that Ash owns. The first is Gary who owned a Blastoise. It could also be noted that both Pokémon were the rival's starter Pokémon, they are both turtle-like Pokémon, they both were seen for the first time in their final form, have never been seen in their mid-evolved forms which are also seen to be owned by a main character and were seen in their first form in flashbacks.
