Ash Ketchum has had many rivals throughout the Pokémon anime, but only one trainer can be his most important rival. Ash Ketchum's journey to becoming a Pokémon master has taken him to many different regions, where he encountered many different Pokémon trainers. However, not every trainer has affected him the same way. Some were only present for one episode, while others became recurring characters and helped Ash develop as a Pokémon trainer.

Some of these rivals were present in the Pokémon games - Gladion, for instance, was a main character in the Pokémon Sun & Moon games. Other characters, like Alain and Paul, appear only in the anime but became vital pieces of the story in their respective seasons. Ash's rivalries have been a focus of the Pokémon anime's formula since it first premiered, and each of Ash's rivals has consistently been compared to Gary Oak, Ash's very first rival.

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It's interesting to note that the latest iterations of the Pokémon anime, Pokémon Journeys and Pokémon Master Journeys, haven't given Ash an obvious rival. There are certain trainers he wants to battle, to be sure, but few who show up to serve as a true rival for Ash. Bea, for example, the Galar region's fighting-type Gym leader, is a great sparring partner for Ash, but their competitive spirit doesn't reach the same heights as it has done with some of Ash's previous rivals. This change in formula might be due to Ash's win in the Pokémon League Conference in the previous generation of the anime. Since it took seven journeys across seven regions for Ash to win a Pokémon League, it's interesting to take a look back at five of the most impactful rivalries that shaped him as a trainer and prepared him for his grand victory.

Kanto & Johto's Gary Oak

Gary speaks to Ash in the Pokémon anime.

Gary Oak, Professor Oak's grandson, was Ash's very first rival. They bickered and battled one another throughout the first two generations and regions of the Pokémon anime. Gary is one of the reasons that Ash became so determined as a trainer. Gary's constant taunting of Ash, whether it came to how easily he defeated certain Pokémon Gyms, or how quickly he caught large quantities of Pokémon, all worked as motivations for Ash to become a stronger trainer. Ash eventually managed to beat Gary in the Silver Conference in Johto.

In terms of power and skill, Ash and Gary are quite evenly matched. Gary is a well-rounded trainer, however, and his role as a Pokémon researcher has provided him with knowledge and insight that few of Ash's other rivals possess. Gary, interestingly enough, now acts as a rival for Goh, Ash's newest friend and traveling companion in Pokémon Master Journeys. Both Gary and Goh are vying for a place in Pokémon's Project Mew, proving that Gary, in comparison to some of Ash's other rivals, is still developing as a character.

Pokémon Diamond And Pearl's Paul

Pokemon Trainer Paul from the Diamon and Pearl anime

Paul was Ash's rival in Pokémon Diamond and Pearl and is one of Ash's most ruthless rivals to date. What made this rivalry so interesting was their opposite approaches to Pokémon training. Ash was caring and creative, while Paul was intimidating and technical. They initially despised each other for those very reasons, and Ash's dislike of Paul grew exponentially when he learned that Paul had abandoned multiple Pokémon, including the Sinnoh fire-type starter Pokémon Chimchar. Paul had taken on Chimchar as a Pokémon because of its unique ability "Blaze," but when he failed to train the fire-type how to use this ability properly, Paul kicked it to the curb. Ash, as a Pokémon trainer, provided enough encouragement to raise Paul's old Chimchar into a fully evolved Infernape, who to this day is one of Ash's strongest Pokémon partners.

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Paul begrudgingly respected Ash's endeavors with his old Chimchar in the end and came to recognize that Ash's style as a trainer had more merit than he initially believed. Ash even managed to beat Paul in the quarterfinals of the Lily of the Valley Conference. The difference in training style between these two trainers is what made them so compelling as rivals. Ash learned a lot from Paul and his Pokémon, especially regarding the needs that different Pokémon have when they evolve. Paul, likewise, learned from Ash that befriending your Pokémon doesn't make you weak - it's more likely to boost your Pokémon's confidence and power.

Pokémon XYZ's Sawyer

Pokémon Trainer Sawyer in the XYZ anime

Sawyer was a trainer in the Pokémon XYZ anime series who greatly admired Ash. Ash's Pokémon team in Kalos is one of the strongest he has ever had, and his rivalry with Sawyer was one of the reasons Ash and his team were able to develop so much throughout the anime. Though Ash beat Sawyer nearly every time they battled, Sawyer understood that he could learn from Ash's creative battling style, and he finally learned to enjoy himself during a Pokémon battle, letting go of his analytical side.

The mutual respect between these two trainers elevated this rivalry. It wasn't based on revenge or proving the other wrong - it was simply about being Pokémon trainers, being on a journey, making friends, and learning along the way. Sawyer's development as a trainer was proven when he finally managed to beat Ash before they met again at the Pokémon League, and their semi-final battle in the Kalos League is one of the most exciting battles in the XYZ anime.

Pokémon XYZ's Alain

Pokemon Trainer Alain in the XYZ anime

Alain, similar to Sawyer, is another one of Ash's friendly rivalries. One of the reasons that Ash is so interested in Alain as a trainer is his Mega-Charizard, and one of the reasons that Alain is so interested in Ash is because of Ash's Greninja, with the "Battle Bond" ability to transform in the middle of a battle. Alain's battles with Ash even convinced him that he should enter the Pokémon League Conference, something he'd never considered before. Alain is an incredibly proficient trainer, and his match against Ash in the finals of the Kalos League is one of the most exciting battles in the entire history of the Pokémon anime. Though Alain managed to beat Ash in the League, few rivals managed to get Ash as riled up and excited for a Pokémon match as Alain did.

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However, what makes Alain such an interesting rival for Ash is the underlying tension of Alain's secondary plotline. He was unwittingly helping Lysandre, the leader of Team Flare, in his plan to destroy and rebuild the world. Though Alain merely wanted to help his friend Marin's Pokémon Chespin, he had a hard time releasing himself from Lysandre's grip, but it was his friendship and rivalry with Ash that finally allowed him to see right from wrong. In the end, he was vital in helping Ash and his friends defeat Lysandre and save the Kalos region.

Pokémon Sun & Moon's Gladion

Gladion, Pokemon Trainer in the Sun and Moon anime, Ash's rival

Gladion is the only trainer here directly from the Pokémon games. His character not only serves as a rival for Ash but also a vital part of the overarching story in Pokémon Sun & Moon. His history with Ultra Beasts provides interesting character development throughout the anime, as he goes from a reserved, closed-off, and somewhat arrogant Pokémon trainer to one who is remorseful, kind, and determined.

Gladion and Ash are on equal footing when it comes to their skills as Pokémon trainers. Both of them have a Lycanroc, though in different forms, and the rivalry between Ash and Gladion is reflected in their Lyncarocs’ rivalry too. Additionally, Ash managed to beat Gladion in the Pokémon League, despite having lost to him plenty of times before, which lead to Ash's first proper victory in a Pokémon League Conference.

Who Is Ash Ketchum's Most Important Pokémon Rival Of All-Time?

Pokémon trainer Paul and his Electivire

Though each of these rivals has taught Ash Ketchum valuable lessons as a Pokémon trainer and aided his development as a character, there is one rival who truly stands out. Paul, Ash's rival in Sinnoh, played a part both in Ash's determination to get better and stronger as a trainer and taught Ash that different Pokémon have different needs. In return, Ash taught Paul that caring for and befriending Pokémon isn't a sign of weakness but of strength. There are very few trainers that affected Ash the same way Paul did. Their battles, arguments, and ethical differences made them proper rivals, and their final respect and admiration for one another truly proved that this rivalry helped both characters grow, not just as trainers but as people too.

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