Professor Kukui is a major supporting character in the anime series Pokémon Sun & Moon. He is the Pokémon Professor of the Alola region and works as a teacher at the Pokémon School on Melemele Island, where he instructs a small class of young Trainers, including Ash Ketchum. His chosen field of research is the study of Pokémon moves and battle techniques, a subject that has fascinated him since childhood, and he is known for his hands-on approach to his work, sometimes even testing attacks on himself to understand them better.

Kukui has an energetic, warm, and approachable personality. Unlike the more formal researchers often associated with the role of a Pokémon Professor, he is casual and direct, speaking with enthusiasm and occasionally weaving the names of Pokémon moves into everyday conversation. He is recognizable by his relaxed style, typically wearing a cap, shorts, and an open white lab coat, and he carries the athletic presence of an experienced battler. Behind his laid-back manner, he is deeply committed to his students, his research, and the people he cares about, and he takes his duties as both educator and scientist seriously.

In his youth, Kukui took part in Alola's island challenge alongside his childhood friend Molayne. He later traveled to the Kanto region to compete in the official Pokémon League there, where he earned the right to challenge the regional Elite Four and was ultimately defeated by the Dragon-type specialist Lance. That defeat left a lasting impression on him and fueled his long-held ambition to establish a Pokémon League in Alola, giving Trainers from his home region an official championship of their own.

When Ash Ketchum arrives in Alola at the start of the series, Professor Kukui welcomes him, offers him a place to stay in his home, and provides him with a Rotom Dex. He also invites Ash to join his class at the Pokémon School. From that point onward, Kukui serves as Ash's mentor and guardian during his time in the region, offering guidance, training, and steady support. Their relationship develops into one of the defining connections of the story, with Kukui treating Ash almost as a member of his own family.

Beyond his academic work, Kukui lives a double life as the Masked Royal, a masked competitor in Alola's Battle Royal tournaments. In this persona, he is a celebrated and powerful fighter, often taking on several challengers at once in the arena. His main partner in these battles is Incineroar, a Fire-type Pokémon that has been with him since it was a Litten in his childhood. Incineroar shares many of Kukui's mannerisms and proves to be a formidable battler, developing a notable rivalry with Ash's Torracat as the series progresses. Kukui also commands other strong Pokémon, including Braviary, Lucario, Venusaur, and Empoleon, and he is highly skilled in the use of Z-Moves, powerful techniques powered by Z-Crystals.

Professor Kukui's personal life forms an important part of his character as well. He is married to Professor Burnet, a fellow researcher, and their wedding during the series brings together the people closest to him. He maintains a close friendship with Molayne and works at the Pokémon School under the supervision of Principal Samson Oak.

Throughout the series, Kukui experiences clear development. He grows from a researcher with a dream into the founder and organizer of Alola's first Pokémon League, a project that represents the fulfillment of his lifelong goal. In the league's final battle, he faces Ash directly in an exhibition match, demonstrating the skill he has built over years of battling and acknowledging Ash's growth as a Trainer. His path also leads him toward marriage and family life, completing his portrait as a devoted scientist, a caring mentor, and an accomplished battler whose knowledge of Pokémon moves and combat makes him a respected figure throughout the Alola region.