Gladion was originally a member of the Aether Foundation together with his mother Lusamine and his sister Lillie. However, over time, he noticed his mother's obsession with the Ultra Beasts and realized that she would ruin Alola if she let Ultra Beasts into the region. For this reason, he decided to leave the foundation, only telling Wicke of his departure. Before leaving, he stole one of the three Type: Null created to be a weapon to attack Ultra Beasts.
Upon leaving the Aether Foundation, Gladion had two goals: to stop his mother and to free Type: Null from the helmet that was meant to subdue it. He eventually worked as an enforcer for Team Skull but was never considered an actual member of the team.
Gladion first meets the player on Route 5 as a Team Skull member, but he does not seem to be interested in Team Skull's affairs, unlike the Grunts near him. After his second battle with the player at the Battle Royal Dome, he realizes the player might be able to help him stop Lusamine. When encountered on Route 13, he informs the player Team Skull is after Cosmog. Knowing now Team Skull is helping Lusamine get Cosmog back, he tells the player that they should make sure Cosmog is safe. When Lillie gets captured while the player is battling Guzma in Po Town, Gladion appears before the player upon their return to the Aether House and battles them to express his frustration. After getting his priorities straight, he takes the player and Hau to Aether Paradise to face Lusamine and save both her and Lillie. Gladion is also encountered on the way to the newly finished Pokémon League on Mount Lanakila. He thanks the player for stopping Lusamine and reveals that not only has he received a Z-Ring, but also managed to release his Type: Null from its restraint, evolving it into Silvally. His Silvally will be holding the memory of the type that is strong against the player's starter Pokémon's type.
After the player has become the Champion of the Alola region, Gladion has taken over as acting president of the Aether Foundation while Lusamine is away. He may be spoken to at Aether Paradise's conservation area, where he will give the player a Type: Null of their own, along with all of Silvally's memory drives.
Gladion's role is mostly similar as in Sun and Moon, although with several changes. As Lusamine is not obsessed with Ultra Beasts in this continuity, he instead left Aether Paradise with Type: Null due to Mohn's disappearance, seeking to become stronger to protect Lillie and Lusamine. After the player becomes Champion, Gladion leaves the Alola region to train at Kanto and Johto. Before leaving, he leaves a Type: Null and a set of memory drives in the possession of Wicke, who gives them to the player at Ancient Poni Path during the post-game.
A month after UltraNecrozma's defeat, Gladion returns to Alola and can be faced in a Pokémon League Title Defense battle, where he will wield the fully evolved form of a Kanto starter Pokémon, whose type matches the player's starter Pokémon's type. After Gladion has been defeated in a Title Defense battle, the player can visit Aether Paradise to see Gladion witnessing a meeting between Lusamine and Mohn, with Lusamine letting her amnesiac husband continue his life of running Poké Pelago. Gladion asks Lusamine if she's sure about wanting to leave him in his current state, but Lusamine is simply satisfied to see Mohn being happy with his life.
In The Announcement and the Prize, Gladion faced against Hau. When Hau mentioned he joined the tournament because he thought it'd be fun, Gladion called him weak and won the battle. In The Party Crasher and Guzma the Destroyer, Gladion's next opponent was Moon, who wanted to know about the Ultra Wormhole. Gladion agreed to tell her about it, but only if she managed to defeat him. Despite Moon's skill, Gladion eventually won the battle through luck.
In The Final Match and a Surprising Finale!, Gladion and Sun faced each other in the finals. During the battle, Sun's attitude annoyed Gladion, who questioned the boy's motivation for joining the tournament. Gladion's words angered Sun, who accidentally activated a powerful Inferno Overdrive that defeated Type: Null before passing out from exhaustion. Though Gladion still had an active Pokémon, Sun was declared the winner. Afterward, Gladon left to find a place to train so he may prepare to face the Ultra Beasts, mentioning that he lost his chance to meet the tapu.
In Homecoming and the Brilliant Professional Golfer, Sun and Moon found an injured Kiawe, who was attacked by Gladion in order to learn where the Ruins of Life were located. After healing Kiawe, the three traveled to the ruins, where they found Gladion trying to take Tapu Lele, who was healing from injuries it sustained from an earlier clash with a Xurkitree. Realizing Gladion wanted Tapu Lele to help fight off the Ultra Beasts, Moon suggested they work together. Sun refused to team up with someone who works for villains and decided to defeat him with his newly-mastered Z-Move. Due to not having a Z-Ring, Sun attempted to borrow Kiawe's, but it was destroyed by Type: Null before he could take it. Although Gladion claimed Sun wouldn't have won even with the Z-Move, a voice appeared, claiming that Gladion wouldn't have destroyed the Z-Ring if he believed that. The voice is revealed to be Kahili, who has her Pokémon distract Type: Null before delivering Sun his own Z-Ring.
In Unleashing the Incredible Z-Move, Sun and Dollar fired a perfected Inferno Overdrive at Type: Null, causing its mask to crack. After switching for Porygon, Sun tried the Z-Move again, but failed, leading to Dollar's defeat. Gladion gave up on Tapu Lele, declaring it too weak to help him with the Ultra Beasts. As he left, Gladion revealed that something must be trying to break into their world through the wormholes.
In Flash and Cosmog's Secret, Gladion arrived at Po Town. There, he was attacked by the Team Skull Admin, Plumeria, who wanted to see if Gladion was skilled enough to be an Enforcer. Though Gladion proved himself, his negative attitude angered Plumeria to the point where she refused to accept him as a true member of Team Skull. When Plumeria told Gladion to follow her, Gladion complied, but was momentarily distracted when a ZygardeCore jumped past him.
In Truth and the Mastermind Behind Team Skull, Gladion appeared at Po Town to battle the Ultra Beasts that Guzma summoned with the Cosmog he received from the Aether Foundation. Gladion revealed Guzma was being used by the Aether Foundation president, Lusamine, so she could create a paradise for herself and the Ultra Beasts she covets. Guzma rejected Gladion's accusation, but was captured by a Nihilego and dragged into a wormhole. The other Ultra Beasts escaped from Po Town's barriers, allowing them to wreak havoc on the rest of Ula'ula Island. When the Captains asked Gladion how they could help, Gladion refused to help and said they wouldn't be of any use before riding off with Type: Null.
In Battle in Vast Poni Canyon, Gladion and Lillie traveled through Poni Island. Gladion revealed he planned on getting the Legendary Pokémon Solgaleo and Lunala to help him destroy the Ultra Beasts. As they traveled, a Xurkitree appeared and attacked them. Gladion and Silvally fought Xurkitree, but Nebby flew out of his hands and met with another Cosmoem. After Xurkitree was defeated, Lillie and Gladion met with Sun and Hapu. They learned that the Sun and Moon Flutes were a pair meant to played at the Poni Altar. The guardian deities of Alola appeared and took Sun and both flutes to the Poni Altar while Lillie, Gladion, and Hapu chased after them.
In Summon the Emissaries of the Moon and the Sun, Gladion and Lillie helped Anabel corner and capture Faba. At the Altar, Gladion and the others found that Sun and Moon managed to evolve Nebby and the other Cosmoem into Lunala and Solgaleo, respectively. Anabel received a call from Looker, who told her that a large number of Ultra Beasts made their way to Poni Island. While Moon, Gladion, Anabel, and Hapu fought off the beasts, Solgaleo was possessed by a Necrozma that appeared from a wormhole. Necrozma grabbed Sun and dragged him into the wormhole, forcing Moon and Lunala to chase after them.
Six months later, in Adventure in the Dark Dimension, Lusamine disappeared while Faba had managed to take control of the Aether Foundation, running it like a dictatorship. At the Aether House, Wicke told Gladion and Lillie that Lusamine was found on Poni Island playing with a group of Ultra Beasts. Gladion suggested going to get Lusamine, but was told to stay behind as he hadn't fully recovered from the injuries he sustained from being exposed to the energy from Silvally's evolution. Wicke decided the best option was for her to return to Aether Paradise and gather information before making their next move.
In Ray of Light!! Through the Crack in the Sky!, Lillie told Gladion that their father, Mohn, was still alive in Alola somewhere. Hoping that telling Lusamine the information would convince her to return to her old self, Lillie decided to go and meet with their mother. Before Lillie left, Gladion suggested she do so dressed in the clothes she picked for herself, not the ones Lusamine picked for her.
Later, Gladion traveled to Aether Paradise, where he found Moon locked in a cell after Faba captured her. After freeing her, Gladion and Moon confronted Faba, telling him that his plans were over. Faba retaliated by tricking Ryuki into battling Gladion and Moon, buying him enough time to try and escape. Gladion allowed Moon to use Silvally in place of her actual Pokémon, which were taken by Faba and hidden away. While Gladion kept Ryuki busy, Moon went ahead to retrieve her Pokémon and make medicine for Gladion's injuries. After taking down Ryuki's first Pokémon, Gladion called off the battle, revealing Faba was using it as a distraction so he could flee. Once he learned others were fighting the Ultra Beasts elsewhere in Alola, Ryuki ran off to join them. When Silvally returned, Moon was absent, having gone elsewhere with Lunala. Gladion then left to stop Faba from escaping, only to find the man cornered by Sun's Alolan Meowth, Cent, who aimed to make Faba pay for his crimes. Faba's intense fear attracted several Nihilego that emerged from a nearby wormhole. Gladion and Cent were forced to watch as Faba was dragged into the wormhole, his fear turning into happiness as he was affected by the Nihilego's neurotoxins.
Months later, Gladion teamed up with Dulse of the Ultra Recon Squad to traverse through Ultra Space and rescue Faba. Ryuki chose to accompany them, much to Gladion's annoyance.
Silvally is Gladion's first known Pokémon. It was first seen as a Type: Null with its Trainer being entered in an Iki Town festival tournament. While the competitors in the tournament were being picked, Gladion was temporarily away due to Type: Null sensing a crack in the sky. During the tournament, Type: Null was called out to battle Hau's Komala, which it defeated. In the final round of the tournament, Type: Null battled Sun's Cent and Dollar. Although it easily defeated Cent, Dollar was able to defeat Type: Null with a powerful Inferno Overdrive. It later evolved into Silvally to protect Lillie from an attacking Guzzlord.
Porygon is Gladion's second known Pokémon. It was first used at the Iki Town festival tournament, where it battled Hau's Pichu. Eventually, it won, forcing Hau to switch for his Komala. In the next battle, it fought Moon's Alolan Grimer and Mareanie, with both battles ending in Porygon's victory.
Gladion held on to Nebby (Japanese: ほしぐもちゃんHoshigumo-chan) for a while as he and Lillie traveled to the Poni Altar. During a battle with a wild Xurkitree, Nebby flew out of Gladion's hand, where it met with another Cosmoem.
Gladion's Pokémon Cards listed with a blue background are only legal to use in the current Expanded format. Cards listed with a silver background are legal to use in both the current Standard and Expanded formats.
Only in Ultra Sun and Ultra Moon, if the player character picks Litten as their Starter Pokémon, Gladion's Lucario will be level 55 during the battle at Mount Lanakila, while it will be level 53 if either Rowlet or Popplio was chosen.