The original Pokémon anime series, Indigo League, set the tone for one of the most lucrative franchises in the world, depicting young Ash going through a series of trials to become an elite trainer. This first season and the Kanto region in which it is set are iconic to this day, introducing several memorable characters – both people and Pokémon.

This led to Ash's recent graceful exit from the show and passing the mantle to Liko and Roy from Horizons anime so impactful. Between battling Gym Leaders who would become lifelong friends and ascending to the Pokémon League, many Indigo League battles have important narrative stakes.

10 Gray vs. Brock paved the way for more than a gym badge

Gym Leader Brock will always stand out for a long time Pokémon fans for his place in the video games and anime. He is the first Gym Leader in both, and his battle with Ash is even more significant than earning a Badge. Not long after bonding with his initially rebellious Pikachu in the heartwarming first episode of Indigo LeagueAsh tries to challenge the Pewter Gym Leader, but is easily defeated.

However, after consulting with Brock's father and doing some soul-searching, he comes back stronger and defeats Brock against all odds. Electric-type Pikachu defeating the dual Rock/Ground-type Onix will always be a defining moment in the anime. Additionally, the trainers become close friends and traveling companions throughout Kanto, rounding out the main cast with Misty.

9 Gray vs. Misty puts the spotlight on the Water-type leader

Misty is another long-time fan-favorite supporting character. Pokémon fans. Despite being the second Gym Leader in Kanto, Ash meets and befriends her before Brock, with their inevitable Gym battle coming two episodes after meeting the Rock-type specialist.

Misty is hesitant to visit Cerulean City when Ash decides to take on the Gym challenge. It is later revealed that she is a Water-type Pokémon Leader and one of the four sisters who run the Gym. Aside from the dramatic battle between Ash and Misty as rivals, this episode is a welcome dive into the latter's character. It explores her insecurities and doubts, making their conflict and growing bond feel all the more meaningful.

8 Gray vs. AJ humiliated the trainer in an informal gym

Being as young as he was, it was expected that Ash would eventually let his pride go to his head. After defeating his opponents who became traveling companions and friends, the protagonist becomes overconfident until AJ's unauthorized gym humbles him.

Watching Ash go through the hardships required to learn what it means to be a well-rounded person made him relatable to younger audiences. The protagonist spoke ill of those with lesser badges than him, but the promising AJ and his Sandshrew gave him a well-deserved beating. Ultimately, this brings Ash back down to earth, leaving him with a parting lesson and a new friend.

7 Ash vs. Lt. Surge was a milestone in Ash and Pikachu's relationship

Episode 14 of Pokémon: Indigo League was a major milestone in Ash and Pikachu's dynamic. They faced arguably their toughest fight at that point against Lieutenant Surge, Vermilion City's Electric-type Gym Leader. Fittingly, the battle pits Ash's Pikachu—who is staunchly opposed to evolution—against Surge and his fearsome Raichu.

It was a tense battle of ideals, with Lieutenant Surge and Raichu's ruthlessness initially overwhelming Ash and Pikachu. This resulted in some serious soul-searching on the part of Ash and Pikachu, questioning whether they should stick to their principles and let the electric mouse remain as is or evolve it with a Thunder Stone. They made the difficult but correct decision, with Ash accepting Pikachu's sense of self and defeating Surge on his terms.

6 Gray vs. Damian justice was served

Another devastating episode of Pokémon: Indigo League was the story of Ash first meeting the beloved fire-starter Charmander. Ash, Brock, and Misty discover Charmander injured and abandoned during their travels, learning that his cruel trainer abandoned him for being weak. The trainer was a spoiled and cruel boy named Damian, who thought that neglecting his Charmander would make the Fire-type creature stronger.

Portraying Damian as a villain was an effective way to educate young audiences about the issue of real-world animal abuse. Through the compassion of Ash and company, Charmander is deservedly nurtured and freed from Damian's callousness. Ash defeats the pompous trainer through the co-led efforts of Pikachu and Charmander, creating a cathartic battle and justice well served.

5 Gray vs. Erika taught the protagonist new respect

When Ash, Brock, and Misty arrive in Celadon City, the protagonist is determined to face its resident Gym Leader. The Grass-type Pokémon specialist leads the Gym, with Ash initially being banned for making derogatory comments about wearing perfume. This leads to a series of antics alongside Team Rocket, with Ash desperate to return for a challenge.

Ash and Erika eventually face off in a three-on-three battle, with the leader frustrating Ash's team. Charmander, Bulbasaur, and Pikachu all face off against each other, but beyond the moment-to-moment struggles, this is a prime example of the protagonist learning a newfound respect. It's only after respecting his opponent, rescuing Pokémon from a fire, and showing more empathy for his team's struggles that Ash earns the Gym Badge.

4 Ash vs. Sabrina was a sinister twist on gym leader battles

The multi-episode story arc about Ash facing off against Psychic-type specialist Sabrina has taken a surprisingly dark turn—or at least as much as a children’s cartoon can. When the aspiring Pokémon master’s ambitions take him to Saffron City, he and his friends find themselves embroiled in a sinister nightmare scenario that can’t be resolved in battle.

The Psychic-type Gym Leader communicates unsettlingly through a doll, initially defeating Ash and sending the miniaturized group to Sabrina's dollhouse. The supernatural horror elements and Ash defeating her with a newly-friended Haunter made for an engaging three-episode arc and a unique twist on the Gym Battle trope. Turning these episodes into part of a story about Sabrina's unresolved childhood trauma also gave this plot an interesting angle.

3 Gray vs. Koga tested the trainer's courage

Koga has always been one of the most striking character designs of the Kanto Gym Leaders, with his ninja motif giving him instant appeal. Ash enters the Fushia City Gym and gets much more than he bargained for, with the challenge being much more complicated than a straight-up battle.

The Poison-type Gym Leader pushes Ash and his team to their limits, with the setup being a series of elaborate traps. Team Rocket is thrown into the mix for chaotic and comic relief, but this is one of the Pokémon: Indigo Leagueof the most inventive battles. Ash's battle against Koga and the synergy of their team tests Ash like no other opponent this season. It also subverts the conventions of gym challenges and highlights Koga's eccentric qualities.

2 Gray vs. Jeanette demonstrated an unlikely competitor

The Pokémon League has been Ash's grand goal since the first episode of Indigo League, and the fourth round battle was intriguing in an unexpected way. Ash is becoming increasingly confident in his chances in this tournament, with Jeanette's team of Beedrill and Scyther being efficiently defeated - until her Bellsprout was released.

Bellsprout was a bizarre choice, as it’s just a first-stage Pokémon acting as the clincher in a high-intensity LoL match. However, Bellsprout’s unprecedented flexibility and agility allow it to wriggle around Ash’s team. Even though it lost, it was still exciting to see Jeanette put up a great fight in unconventional ways. It reminded Ash to keep his arrogance in check and appreciate tactical ingenuity.

1 Gray vs. Ritchie gave the young protagonist a learning opportunity

Ritchie is a captivating member of the Pokémon: Indigo League supporting cast of the anime, acting as friendly rivals to Ash. Both fighting to qualify for the upcoming Pokémon League finals, they face off in a tense battle that sees each trainer put to the mental test. Ash and his friends, unfortunately, will have to deal with the antics of Team Rocket on their way to the fifth round.

Ash is exhausted in preparation for his battle with Ritchie, with the latter whittling down Ash's team until only his rebellious Charizard remains. Seeing the main character struggle occasionally is preferable to a hero who never falters. Coupled with the natural tension of two talented friends and rivals in a high-stakes competition, this battle and defeat taught Ash a lesson in discipline.