Professeur Saito, known in English versions as Doctor Saito or simply the mechanic Saito, is a supporting character in Tiger & Bunny who works as an engineer for Apollon Media, the company that manages the city's sponsored superheroes. His primary responsibility is developing and maintaining the powered suits worn by the heroes, and he is specifically credited with creating the new armored suits used by Barnaby Brooks Jr. and Kotetsu Kaburagi, the hero known as Wild Tiger. In this capacity, he operates behind the scenes as the technical backbone of the hero system, ensuring that the fighters have functional equipment for their patrols and battles.

Saito's personality is marked by a striking contrast in how he communicates. In person, he speaks in a barely audible, respectful voice that can be difficult to hear, but when he communicates over radios and intercoms he becomes loud and outspoken, shouting his messages without hesitation. This quirk makes him memorable in scenes where heroes receive instructions or warnings mid-battle. He is an inventive and detail-oriented engineer who takes evident pride in his craft, though his enthusiasm sometimes leads him in unusual directions. He has a habit of adding upgrades to the hero suits that have little practical use in combat, such as a clock installed on the left arm of Tiger's suit simply for telling time, as well as transforming weapons that appeared to boost the strength of Tiger and Barnaby but were designed mainly for show. These flourishes reflect his playful, theatrical side and his desire to showcase his technology, even when pure function would be more sensible.

Saito's motivations center on his dedication to his engineering work and his role within Apollon Media. He is not a NEXT, meaning he possesses no superhuman abilities himself, but his contributions are vital to the heroes who do. His role in the story is that of a support figure who appears regularly as the heroes visit his workshop for repairs, upgrades, and new equipment. He is one of the few non-hero characters who interacts with the main cast on a consistent basis, and his lab functions as a recurring location where the heroes regroup and prepare for their missions. Because the suits he builds are essential to the heroes' survival, his work often has direct consequences for the outcome of battles, even though he is not present on the front lines.

In terms of relationships, Saito works most closely with Kotetsu and Barnaby, the two heroes whose suits he personally created. His dynamic with Kotetsu in particular carries a note of exasperation, as Kotetsu's reckless fighting style tends to damage his equipment, forcing Saito to repair it. Despite this friction, there is a professional reliance between them, as Kotetsu depends on Saito's technology to continue his work as a hero. With Barnaby, Saito maintains the high-performance suit of a more disciplined fighter, and his precision as an engineer matches the needs of a hero known for his careful approach. Throughout the series and its films, Saito remains a constant presence in the background of the hero world, and his character shows little dramatic change but instead provides stability and continuity. His development is primarily expressed through the evolution of his technology, as he continually refines the suits and introduces new features in response to the heroes' needs. His notable abilities are entirely technical rather than superhuman, encompassing genius-level engineering, suit design, weapon modification, and rapid repair work, making him indispensable to the heroes even though he never takes the spotlight himself.