In its debut appearance as a Turtwig, it is shown to be nice, kind and a street-smart Pokémon who shares other Pokémon's food and giving them some fruits. It is also shown to be overprotective to fellow Pokémon when it protects Pikachu from Ash. This is similar to Ash's Bulbasaur and Brock's Mudkip. Torterra is also shown to settle feuds with angry Pokémon. When it likes the trainer such as Ash and Clara, it is seen to bite their heads in affection much like James' Carnivine and later Ash's Gible when it bites his head.
In The Champ Twins!, Torterra, as a Turtwig, had an initial argument with Dawn's Piplup when Ash and Dawn are arguing at each other during their tag battle against The Champ Twins which resulted in their first loss. Both continues to argue until Pikachu breaks up by hitting them with a Thunderbolt. Both of them later teamed up to fight Team Rocket's Pokémon and finally against The Champ Twins and the two became best friends, after both Ash and Dawn win.
Torterra has a very close relationship with both Ash and its teammates, especially with Pikachu and Infernape, who are its other best friends.
As a Grotle, it retains its pre-evolved personality and showing its determination to train harder by itself as seen in Aiding The Enemy!. Grotle also makes friends with a wild Snover in The Lonely Snover and they had share their innate ability to grow Snover berries and Grotle nuts.
As a Torterra, its behavior is similar to Paul's Torterra and retains its determination while it was a Grotle and can defend fellow Pokémon from any attacks as possible as seen in The Fleeing Tower of Sunnyshore!. However, it actually feels sad about its lower speed.
Torterra was first caught as a Turtwig after battling Ash and his Pikachu. In its debut appearance, it manages to save Pikachu from Team Rocket and also shows its overprotective nature when protecting Pikachu from Ash. Turtwig is also friends with an old lady named Clara and its affection is to bite someone's head like Ash while showing affection to Clara when she blocks it with just a long twig. After Team Rocket is blasted off, Turtwig decides to challenge Ash using Pikachu to fight but was defeated and allows Ash to capture it. Clara tells Ash to take good care of Turtwig. Turtwig is also used by Ash while fighting against Paul's Chimchar. It also displays its intellectual skills to fight an opponent until it was being defeated it. Paul shows his cruel side to Ash when he defeats him in battle even his mistreatment to his Pokémon.
In The Grass Menagerie!, Turtwig battles Gardenia's Turtwig after it loses the battle against her in their first bout upon meeting. Both are equally matched even it got a disadvantage when it was hit from its Leech Seed. Turtwig eventually heals itself from its Synthesis as both of them charge head on using Tackle. Turtwig manages to defeat Gardenia's. Therefore, Turtwig was easily defeated by Gardenia's Rosarade in one hit using Weather Ball causing Ash to use Aipom as his final Pokémon to fight until it defeats it.
In some episodes, Ash does his best to train Turtwig of learning Energy Ball until in the episode, Riding the Winds Of Change!. Ash tells Turtwig to use Energy Ball against Team Rocket when they attempt to steal all the Gligar. Turtwig finally masters this move when it focuses on using its full extent of its power and unleashes it to hit Team Rocket's Meowth Balloon to blast them off.
In Aiding the Enemy!, Turtwig trains along with Dawn's Pokémon along with Ash's Pikachu, Buizel and Chimchar. When Paul arrives to see them while he was with Brock, Chimchar was afraid to see Paul again as both Piplup and Turtwig defend it. Turtwig battles against Paul's Honchkrow but it was attacked by its attacks multiple times. Turtwig, desperate to fight against Honchkrow, evolved into Grotle, but lost due to its lowered Speed and unable to move due to its heavier size. When Honchkrow defeats it, Paul's Torterra was watching the whole time while being groomed by Team Rocket who is disguised as Gardeners to tend its trees from its shell. It also convinces Paul during its practice to help Ash's Grotle but he tells it to let them be. As everyone is asleep, Grotle decides to train itself to gain its speed but failed as it cries and was found by Pikachu, Buizel, Chimchar and Gliscor while Piplup, Staravia and Croagunk tries to wake Ash, Dawn and Brock. The group are confronted by Paul's Torterra which it allows Gliscor to attack both X-Scissor and Steel Wing at it but Torterra does a Body Slam but spares Gliscor when unleashes its Frenzy Plant. Torterra did this as a pointers for Grotle to fight on the ground rather than speed before walking away back to its trainer, Paul who remarks how curious it is. With that, Ash decides to train Grotle to fight on the ground after Paul's Torterra's advice to help Grotle fighting on the grounds.
Grotle became friends with a wild Snover in The Lonely Snover when it spends time with Ash and his friends along with their Pokémon. After Ash and his friends are done eating breakfast, they discovered Grotle had grown several nuts from the trees in its shell as Brock states that it was the adjustment to Grotle's evolution and all of the wild Pokémon are here to eat its nuts. Suddenly, both Grotle and Snover are captured in the cage by Team Rocket for the second time after they fail the first time. Pikachu tries his best to release them with Thunderbolt but it was unaffected and Grotle manages to get free with Energy Ball except Snover. When Ash and his friends chase Team Rocket's Meowth Balloon, Grotle tries to follow them but it got tripped due to its heavier size. Grotle becomes desperate to rescue its friend, he learns Rock Climb as it climbs faster to save Snover and manages to destroy the balloon to blast Team Rocket off. Grotle also saves Snover while he catches it to Brock's Happiny to safety and soon becomes tired after saving it.
Since evolution, Grotle managed to defeat Candice's Sneasel but lost to her Abomasnow.
Grotle is among of Ash's Pokémon are in a bad shape after he lost to Paul in the first Full Battle. After Pikachu is rescued while Team Rocket are blaming each other, Ash commands, Staraptor, Buizel, Grotle, Pikachu, Gliscor and Monferno to blast Team Rocket off with their powerful abilities after Ash fully restores his confidence and determination from his first loss.
In The Fleeing Tower of Sunyshore!, during a Gym Battle against Volkner, Ash uses Grotle to fight Volkner's Luxray which got postponed soon after it was caused a black out even his electric creations as well. As they get out of the Gym in a manual situation, Volkner was informed by Officer Jenny that all of the electricity of the Sunyshore City was cut off. Volkner decides to investigate the matter after he tells Ash and his friends and Flint about the Solar Power he had made for the city until Team Rocket shows up at the top of the tower to confront them. They reveal that they are here to steal the Sunyshore Tower which it manage to steal by moving heavily in wheels. Volkner would never allow someone to get his tower, he chases Team Rocket followed by Flint along with Ash and the group to stop them. By the time they arrived, Team Rocket had modeled the Sunyshore Tower into a rocket tower. As it started to blast off, Ash, Flint and Volkner manage to hang on the rocket leaving Brock and Dawn behind. However, Flint falls into the rocket and land into the water. Only Ash and Volkner are able to enter inside the tower. Upon going to the observatory, they got caught in the cage even both Pikachu and Raichu's electric attacks are negated due to absorbing electricity from the tower. With no other choice, Ash releases Gible to smash the bars from the cage with Rock Smash to free them and attacks Team Rocket at the same time with its Bite. James and Jessie release both Carnivine and Seviper to attack both Raichu and Pikachu. Despite their efforts to electrocute them it got attacked quickly with both Vine Whip and Poison Tail forcing Ash to use Grotle to attack Team Rocket's Pokémon with Tackle and eventually evolved into Torterra while defending both Pikachu and Raichu and knocks their Pokémon with its newly learned Leaf Storm and finally blasts Team Rocket off with another Leaf Storm. Torterra was watching Pikachu, Raichu and Luxray with their Thunder ability to keep the electricity at bay while Volkner did his best to return the tower back to the city. After the tower is restored but with light damage, Dawn was amazed to see Torterra even in her Pokédex. Volkner tells Ash that he needs some time to repair the tower and their Gym battle as Ash accepts and decides to keep training while Flint cheers Dawn to win the Grand Festival.
With its new size and strengths, Torterra now knows more powerful moves such as Leaf Storm in addition to the moves Energy Ball, Rock Climb and Synthesis. Despite its size and power, it has no problems battling Team Rocket, but it has been defeated in several battles against Pokémon it should have an advantage over: Volkner's Electivire, Bertha's Hippowdon and Paul's Drapion, though most likely because not only did they have moves that Torterra was vulnerable against, but they also had better maneuverability over it and its massive size made it an easy target. Also even when it lost, it managed to at least put up a close fight.
Ash finally use Torterra again during the final battle against Team Rocket's Pokémon while teaming up with Ash's Pikachu, Dawn's Piplup and Brock's Sudowoodo before they leave back to Kanto and Torterra uses both Leaf Storm and Energy Ball to hit them before blasted off by Pikachu and Piplup's Volt Tackle and Hydro Pump combination.
Ash decided to leave Torterra at Professor Oak's Lab when he made a fresh start for Unova. It currently resides at Professor Oak's Lab.
- When it was a Turtwig, Torterra has a way of showing affection by biting on someone's head.
- Torterra is the only Pokémon in Ash's Sinnoh team that has never defeated any of Paul's Pokémon.
- Throughout its evolution, Torterra has relied on specific stats to battle.
- As a Turtwig, Torterra relied on speed, accuracy, and evasiveness.
- As a Grotle, Torterra relied on defense, patience, and precise attacks.
- As a Torterra, Torterra relied on attack power, strength, and healing.
- After evolving from Grotle to Torterra, it was the first time Ash had two fully-evolved starter Pokémon from the same region.
- Torterra is the second fully-evolved Grass-Type Starter Pokémon Ash owns; Sceptile is the first.
- Torterra is Ash's first Pokémon to learn a Hidden Move, Rock Climb.
- Ash's Torterra is the first Pokémon Ash has owned that he still now owns that has a unique type. His second being Krookodile and the third being Hawlucha.