Squirtle first appeared in Here Comes the Squirtle Squad, being the leader of a gang known as the Squirtle Squad, a group of rogue Squirtle who were deserted by their Trainers. Meowth managed to befriend the Squirtle Squad by convincing them that Jessie and James were his pets. The Squirtle Squad then captured Ash, Misty and Brock so they could take Pikachu back to Meowth. Ash managed to convince the Squirtle Squad to let him free to get a Super Potion for Pikachu, who was badly injured after an earlier encounter with a Goldeen. The Squirtle Squad agreed to let Ash go to town to buy a Super Potion, but if he didn't return by noon the next day, they threatened to dye Misty's hair purple (in the original, they threatened to kill her).
Squirtle saving Ash, after Ash had done the same
When Ash got back with the Super Potion, Team Rocket began bombing the Squirtle Squad after they received Pikachu. Ash, Misty, and Brock ran to hide in the Squirtle Squad's cave; however, when Ash noticed that the leader was stuck on its shell, he went back to save it, shielding Squirtle's body with his own. Dazed and with more bombs en route, Ash told Squirtle to save itself. So touched by Ash's loyalty, Squirtle burst into tears, summoned enormous strength, and carried Ash to the safety of the cave. Squirtle then defeated Team Rocket with Water Gun. However, Team Rocket's bombs had started a forest fire, which the Squirtle Squad worked together to put out. After putting out the fire Officer Jenny appointed the Squirtle Squad as the official firefighters of the town. The leader of the Squirtle Squad preferred to join Ash on his journey rather than fight fires alongside his group, as it wanted to repay Ash for saving his life during the bombing. After being accepted, it happily ran into Ash's arms, as the Trainer declared he had caught a Squirtle.
During its time with Ash, Squirtle became one of Ash's three most trustworthy Pokémon, next to Pikachu and Bulbasaur, and it was used often. Squirtle's Water type and ability to swim helped Ash in a few choice circumstances, notably the escape from St. Anne in Pokémon Shipwreck.
Squirtle bearing Pikachu across the water
It served as Pikachu's 'steed' when the group competed in a race in Ash's place (Ash having taken Lara Laramie's place on Ponyta). The two were at a significant disadvantage due to Squirtle's short legs and Pikachu's comparative weight, but in a way this helped as they managed to escape the Electrode self-destructing. They made ground when they reached the water stage, putting them in the top four with Ash, Misty, and Dario. However, intervention from Team Rocket forced a battle, and the two were put out of the running by a Glare attack from Arbok.
In Attack of the Prehistoric Pokémon, Squirtle desperately tried to stop a fuse from detonating explosives but failed. This resulted in Ash, Pikachu, and Team Rocket being trapped underground with hostile Prehistoric Pokémon. Only Squirtle was rescued from the rubble by Misty and Brock. It then did its best to rescue its Trainer. In The March of the Exeggutor Squad, it was used in an attempt to con Melvin into believing Ash was able to magically control water and fire with the use of a box that inside contained Squirtle, Bulbasaur, and Charmander, but the three Pokémon began to fight and ruined the trick.
In Beach Blank-Out Blastoise, Squirtle was instrumental in helping rescue a colony of Squirtle, Wartortle and a Blastoise from Jigglypuff.
Squirtle's Gym Battle debut came late and its Kanto Gym record was two losses, the first to Blaine's Ninetales in Riddle Me This, who Ash believed would be disadvantaged against Squirtle. Ninetales' Fire Spin completely overpowered Water Gun and took Squirtle down in one hit. It was then sent out to fight the fire in Volcanic Panic to cool off Onix, Geodude and Pikachu with water as they dammed the volcano. The second loss was against Giovanni's Machamp, under control of Jessie in The Battle of the Badge. Squirtle took damage from Machamp's Karate Chop, but the battle was ended when Giovanni's Pokémon defected and Team Rocket was sent blasting off.
Squirtle landing the knockout blow in the second round of the Indigo League, with its signature finisher, Skull Bash
Ash relied on Squirtle to battle Mandi in Round One - Begin!, but his powerful Kingler took the sweep and Squirtle was unnecessary. However, it won Ash's second round by using Skull Bash to defeat a Nidorino in Fire and Ice after it revealed its ability to use Withdraw to absorb the Nidorino's Tackle.
In Friend and Foe Alike, Squirtle was sent out to battle Ritchie's Butterfree, Happy. However, it was easily put to sleep by Sleep Powder and Ash lost the round.
Squirtle was used more prominently in the Orange Island Gyms, first in competition against Cissy's Seadra in Fit to be Tide. Both Pokémon had to shoot cans with Water Gun, but when they hit the final can at the same time, the match resulted in a draw. Though it did not win, Ash still congratulated it on its admirable work.
In Naval Maneuvers, it joined Pikachu, Bulbasaur, and Ash in steering the ice sled down the mountain, resulting in a win for Ash.
Learning Hydro Pump to overcome Rudy's Starmie
One of Squirtle's most notable battles and its only Gym Battle win was in Misty Meets Her Match. Earlier in the episode, it helped Pikachu and Bulbasaur destroy the targets, before coming out third against Rudy's Starmie. Its powerful Water Gun managed to match Squirtle's, and Rudy's music allowed Starmie to dance away from Squirtle's moves and then use Thunderbolt to knock Squirtle into submission. With encouragement from Misty, Squirtle propelled itself away from Thunderbolt and while using Withdraw learns Hydro Pump to become airborne and hit Starmie hard. Closing the battle with Skull Bash, Ash wins the battle and his third Orange Island Gym Badge.
In The Pokémon Water War!, Squirtle attempted to rescue a warehouse on fire, but when the fire spread, it needed rescuing itself by Captain Aidan and Team Wartortle. This shot Squirtle's confidence as a firefighter and Ash pleaded with Aidan to allow Squirtle to train with his team for a short period. However, they fell into a Team Rocket trap and were captured, but Squirtle's thinking allowed the group to escape: they flooded the cabin to allow mobility, and then tricked Meowth into cutting the nets, before blasting Team Rocket away. Squirtle then joins the effort at a burning apartment and halts the fire, saving the day.
In Hello, Pummelo!, Squirtle was sent against Drake's Onix, who managed to evade Water Gun with Dig and then caught Squirtle with Bind. However, Squirtle broke free with a Withdraw/Hydro Pump combination, then hit Onix with Skull Bash to knock it out. In the next episode, it fought Dragonite, only for its Hydro Pump to be countered by Dragonite's Water Gun. Squirtle was able to use Withdraw in time to evade most of the following Thunderbolt but was still badly hurt. Squirtle used Bubble Beam to hit Dragonite dead-on, but this was the only successful attack and it was beaten by a slam from Dragonite's tail. Pikachu went on to defeat the exhausted Dragonite and Squirtle earned a place in the Orange Islands Hall of Fame.
Squirtle accompanied Ash to Johto as well, the final time it would serve as a permanent member of his team. In Don't Touch That 'dile, Squirtle was used against Team Rocket with Pikachu, Bulbasaur, and Charizard. Combining its Water Gun with their attacks, it fired directly on Team Rocket's Pokémon. In The Double Trouble Header, it was sent out to battle against Team Rocket along with Bulbasaur after they captured Pikachu and Chikorita. During its time with him, it and Bulbasaur showed concern for him on occasions, such as when Ash, Pikachu, and his soon to be caught Chikorita were lost in a snowstorm in The Chikorita Rescue. In Once in a Blue Moon, a Quagsire stole the GS Ball and swam away. Ash tried to run after it but ended up sending out Squirtle to chase it down. After failing to wrestle it out of the Quagsire's mouth, Squirtle used Water Gun, causing the GS Ball it slips out of Quagsire's mouth, and allowing Pikachu to catch it on the shore. While both Quagsire and Squirtle were using Water Gun against each other, Misty tried once again to catch it, but before throwing the Poké Ball, Officer Jenny stopped them and arrested them for violating the Quagsire Preservation Restrictions.
In The Fire-ing Squad!, it competed in an event called the Fire and Rescue Grand Prix, a firefighting competition for water Pokémon. As luck would have it, one of the teams was the Squirtle Squad, but they were confused without their leader. Ash's Squirtle led the Squirtle Squad to win the Grand Prix, and at the end of the episode Squirtle returned to the Squirtle Squad because Ash felt that the old gang needed Squirtle more than he did. It said goodbye to its friends and Bulbasaur extended a vine to its long-time friend, shaking solemnly.
It returned briefly to battle in the Silver Conference after Kingler was badly injured by a group of renegade Voltorb. It joined Totodile and Phanpy against the Fire-type Trainer Macy. It was Ash's last Pokémon, faced with an advantaged Electabuzz. However, Squirtle proved much faster and managed to hit Electabuzz with a series of Water Guns before it could launch any Electric-type moves. A Skull Bash was enough to knock out Electabuzz and even up the match for Ash, leaving just Quilava left. Squirtle used an explosion of moves to cover a stealthy Water Gun, but was hit and knocked on its back by Quilava. As Macy went in for the knockout, Squirtle used Hydro Pump to hit Quilava with water and its own body, sealing the victory for Ash. Squirtle stayed around to watch Ash's Silver Conference battles, and then left in Johto Photo Finish!
While Squirtle made no appearances during the Hoenn arc of the Advanced Generation series, it did make an appearance, along with the rest of the Squirtle Squad, in Of Meowth and Pokémon (Part 2). Squirtle and two other members of the Squirtle Squad ambushed Smoochum and attacked her with a Water Gun, sending her flying.
Kanto Battle Frontier
In Gathering the Gang of Four!, Squirtle returned to help Ash with his final battle against Brandon, meeting May's Squirtle in the process. It expressed happiness in seeing Pikachu and Bulbasaur again and departed with the two, Ash, and Charizard for the woods. Though tension between the group began to erupt, they settled their differences and sat as Ash recalled his meetings with the four of them. After Pikachu was captured by Team Rocket, Squirtle participated in saving his teammate.
In Pace - The Final Frontier!, Squirtle battled Brandon's Ninjask. Squirtle's Rapid Spin successfully deflected Aerial Ace, but Ninjask gained the upper hand by stalling Squirtle with Double Team and hitting with Aerial Ace. Squirtle managed to escape Sandstorm with Hydro Pump, but became blinded by Sand Attack, leaving it exposed to Ninjask's attacks. While the next Hydro Pump missed, the water was able to clear Squirtle's eyes. Squirtle then swiftly unleashed Skull Bash, knocking Ninjask out of the battle. Squirtle was then matched up against Brandon's Solrock. In this battle, all of Squirtle's moves were dodged or blocked by Solrock's Psychic moves. A missed Rapid Spin saw Squirtle crash into the wall, and it was flattened by Solar Beam, causing it to lose the battle. After Ash defeated Brandon, Squirtle returned to the Squirtle Squad.
Squirtle appeared in a flashback in The Fires of a Red-Hot Reunion!, when Ash remembered the night he was stuck in a snowstorm and Squirtle, along with Charmander, Bulbasaur, Pidgeotto and Pikachu, helped keep Ash warm.
Squirtle and some of its fellow Squirtle Squad members reappeared in Alola, Kanto!, being photographed by Rotom.