Althéo is a character from the Pokémon Sun & Moon anime who serves as a Trial Captain in the Alola region, specializing in Normal-type Pokémon. He is a graduate of the Pokémon School, where he is remembered as an exemplary and heroic student, and he has also traveled to the Kalos region for further study. Althéo lives in the largest house in the town of Hau'oli City on Melemele Island with his parents, and his mother, a former actress, is said to have passed on to him a taste for grooming and attention to appearance.

In terms of personality, Althéo is notably coquettish and has a high opinion of himself. He is frequently preoccupied with his looks and style, often making references to hair, shampoo, and salon appointments. Despite this vanity, he is portrayed as a genuinely kind and talented Trainer who believes in a gentle approach to battling. This is demonstrated in his training philosophy, where he politely asks his Pokémon to dodge attacks, emphasizing respect and partnership over aggression. This contrasts sharply with more aggressive Trainers, and Althéo believes that respecting one's partner is the key to success.

Althéo's role in the story begins when he returns to Alola from Kalos, immediately capturing the admiration of the current students at the Pokémon School. He serves as a mentor figure, particularly to the protagonist, demonstrating advanced techniques and the bond he shares with his Eevee. A key part of his backstory involves a longstanding rivalry with Tupp, a member of Team Skull. This rivalry stems from their childhood, where Althéo's popularity, especially with girls, created a deep-seated jealousy in Tupp. This conflict comes to a head when Tupp challenges Althéo to a battle, seeking revenge for past slights. Althéo also participates in the Manalo Conference, successfully qualifying for the quarter-finals during the Battle Royal by eliminating Team Skull grunts and another Trainer. However, he is ultimately eliminated in the first round of the tournament by the powerful Guzma.

Throughout the series, Althéo forms several key relationships. He shares a strong, respectful bond with his partner, Eevee, whom he refuses to evolve, believing in its strength as it is, similar to the protagonist's choice regarding Pikachu. He also shows a deep appreciation for the game of Pokémon Ping-Pong, where he is a champion. In a tournament, he faces a rival named Rageant, whose aggressive and harsh treatment of his own Pokémon contrasts with Althéo's philosophy, ultimately leading to Althéo's victory. His relationship with the protagonist is one of mutual respect, as Althéo shares his knowledge and admires the protagonist's skills.

Althéo demonstrates significant growth in his abilities, having completed his Island Challenge years prior. He is a highly talented and versatile Trainer, possessing mastery over both Mega Evolution and Z-Moves. His signature technique involves a special Z-Move performed with his Eevee, which summons the power of all known Eeveelutions from the archipelago to bolster his attack. Beyond battling, his skill in Pokémon Ping-Pong is another notable ability, showcasing his dexterity and strategic thinking. In the game canon, his battling prowess is further detailed, showing that his team includes powerful Normal-types such as Smeargle, Gumshoos, and a formidable Snorlax capable of using a wide range of attacks like Flamethrower, Surf, and Hyper Beam, further cementing his status as a powerful and well-rounded Captain.