At the beginning, it was assumed that Paul was a Trainer just starting out. However, this was proven wrong in Top-Down Training!, in which he revealed that he had already traveled through Hoenn, Johto and Kanto, participating in their respective League Conferences but failing to win any of them before returning to Sinnoh. In A Pyramiding Rage!, it was revealed that Kanto was the very first region he traveled through.
He first appeared in Two Degrees of Seperation!, although he only made a brief appearance at the ending of that episode; he was fully introduced in the next episode, When Pokémon Worlds Collide!, in which he challenged Ash to a 3-on-3 battle. After the battle resulted in a tie, Paul released one of the three Starly he caught, writing it off as weak, and walked off. He later appeared in Different Strokes for Different Blokes, in which he defeated Ash in a Single Battle after meeting him along the way when exploring Bewilder Forest. He caught his Ursaring in the forest. During the episode, he insulted Ash and especially his Turtwig by calling it pathetic, sparking their rivalry. At this point, Ash realized Paul's strategy of disregarding Pokémon and thenreleasing them if they did not meet his expectations. He also commented that he would not lose to Paul again.
Paul then battled against the Oreburgh Gym Leader Roark in Shapes of Things to Come! and managed to win the Coal Badge. Although he stayed to watch Ash's first battle against Roark in the next episode, he walked off. His style of indiscriminately releasing weak Pokémon was shown again as he gave the Azumarill he used against Roark to a kid in the Pokémon Center after it failed to help him in the battle.
Paul did not appear again until Top-Down Training!, in which he audaciously challenged the Sinnoh League Pokémon Champion Cynthia to a Full Battle. After his first four Pokémon were easily defeated by Cynthia's Garchomp, he surrendered. He briefly appeared in A Maze-ing Race!. He was then a participant in the Hearthome City Tag Battle Competition, in which he was partnered with his rival Ash. Despite winning the quarter-final match, he was very disappointed with his Chimchar and released it, which Ash quickly claimed. Eventually, Paul and Ash managed to win the tournament. Paul then revealed how he captured Chimchar: one day, he ran across it and saw it activating its Blaze Ability to counter a horde of Zangoose that were violently attacking it. Paul was highly impressed and decided to catch Chimchar, but never while it was in his possession did it manage to recreate that powerful Blaze. After winning the tournament, he wrote off the tournament as nothing more than an opportunity to boost his battling skills, giving his Soothe Bellprize to Ash.
He also captured his Gliscor in Riding the Winds of Change!. His next appearance was in Chim - Charred!, in which he battled Ash after engaging in an argument over Ash's true skills as a Trainer. After using his Gliscor to defeat Ash's Gligar with relative ease, he then put his Ursaring against Chimchar. Chimchar had the lower hand for much of the battle, but it was able to easily defeat Ursaring after it activated Blaze. The battle was cancelled when Chimchar's Blaze couldn't be controlled since it was activated out of resentment and a determination to defeat Paul. Paul was impressed as the Blaze appeared much more powerful than the Blaze that drove him to initially capture Chimchar in the first place.
He next appeared in Aiding the Enemy!, in which he used his Honchkrow in a Single Battle against Ash and his newly evolved Grotle, defeating Ash with ease partly due to Grotle being unable to adapt to its loss of speed. This was seen by his Torterra, who later helped Ash's Grotle handle the changes in itsevolution. He also participated in the PokéRinger in Pursuing a Lofty Goal! with his Honchkrow, and made it to the finals but lost to Ash's Staraptor, which was newly evolved.
In his next appearance, A Pyramiding Rage!, much was revealed about Paul's motivation as a Pokémon Trainer and his character. When his older brotherReggie was a traveling Pokémon Trainer challenging the Battle Frontier, he had lost to Brandon. The way Reggie handled the loss is what caused Paul to become a callous person and to be so adamant about strength in battle. Instead of bearing the shame of his loss to Brandon, Reggie moved on with his life and put the loss behind him. Paul found this to be unacceptable, and he became disappointed of his brother. He challenged Brandon to a Full Battle in hopes that he would be able to do what his brother never could. However, Paul lost to Brandon without being able to knock out any of Brandon's Pokémon. Brandon said that this loss was because Paul was unable to control his emotions.
Following Reggie's suggestion in A Pyramiding Rage!, Paul battled Ash in a Full Battle in Pedal to the Mettle! and Evolving Strategies!. Here, he showed his true colors in battle and, despite Ash's Chimcharevolving into Monferno and three of Ash's Pokémon using the Counter Shield strategy, Paul won the match easily with only two of his Pokémon fainting, one of which defeated half of Ash's team nearly single-handedly. He had his Pokémon use a broad variety of strategies, which he kept up his sleeve until this battle, such as tempting Ash to send his Staraptor up against his Torterra so he could attack it with Stone Edge, Electabuzz using Light Screen to aid its comrades, using his Ursaring against Ash's Pikachu so as to activate its Guts Ability, and his Magmortar using Rock Tomb to protect itself against Water-type attacks. As a result, his strategy of completely overwhelming and outsmarting Ash with his more powerful Pokémon team succeeded with excellent results.
In Double-Time Battle Training!, it was revealed that Paul had earned the Mine Badge from Canalave Gym and, by doing so, had collected the eight Badgesrequired to enter the Sinnoh League.
Paul reappeared in Fighting Ire with Fire!, encountering Ash for the first time since their Full Battle. He also met his admirer Barry for the first time; however, Paul wasn't impressed by him and refused his offer for a battle, suggesting he battle Ash instead since he was denying all challenges to go into serioustraining. He later watched the battle between Ash's Monferno and Barry's Empoleon and when Pikachu, Piplup and Empoleon were nearly crushed by one ofTeam Rocket's damaged mechas, he saved the three with the help of his Electabuzz. He then witnessed Monferno evolving into Infernape, who then saved Electabuzz and the other Pokémon from getting crushed. Paul was impressed by Infernape, and gained a little respect for Ash at how well he had raised it. When asked by Ash if they could have another Full Battle, Paul confirmed they would in the Sinnoh League, and that Reggie was looking forward to seeing it.
Paul entered the Lily of the Valley Conference in An Old Family Blend!, in which he was shown in the stadium along with all the other competitors. He passed the preliminary round in League Unleashed! and defeated Barry in the third round in Casting a Paul on Barry! with his superior tactics and the superior power of his Pokémon. His next battle was against his rival Ash in Familiarity Breeds Strategy!, continuing into A Real Rival Rouser! and Battling a Thaw in Relations!. After a fierce battle, Paul was finally defeated, and he and Ash parted on good terms, Ash having earned Paul's full respect. It also seemed Paul had decided to change himself somewhat, as when Electivire was defeated, he thanked it for a job well done; up to this point, this was something Paul practically never did, even if his Pokémon won. Afterwards, Paul stated that his next intention was to return to Snowpoint City and re-challenge Brandon. He briefly appeared in The Semi-Final Frontier!, seeing Ash lose to Tobias.
Privately commenting to Brock and Dawn on the battle between Ash and Paul, Cynthia predicted that they would both be entering the Champion League soon.
Paul made a cameo appearance during the credits of Zoroark: Master of Illusions, in which he was seen visiting a ruin with statues of Dialga and Palkia.