Colbert is a teacher at the Tristain Academy of Magic, distinguished by his bald head and calm, analytical demeanor. He serves as a mentor and a crucial source of support for the protagonist, Saito, being the first to recognize him as the legendary familiar Gandálfr.

His background is layered with a dark and hidden past. Before his life as an educator, Colbert was a powerful and elite mage in the service of Tristain, leading a special magic unit and earning the fearsome epithet of the Flame Snake. It was during this time that he was ordered to carry out a brutal mission that involved the slaughter of an innocent village. This event, which later revealed to be the hometown of the soldier Agnes, became a source of overwhelming guilt that would define the rest of his life.

Haunted by his actions, Colbert abandoned his position and rank. He assumed a new identity as a teacher at the academy, concealing his past in an effort to atone. His personality shifted from that of a soldier to a man deeply dedicated to peaceful, productive applications of his craft. As a square-class fire mage, he could have wielded great destructive power, but instead channeled his genius into invention and science. He is portrayed as more of a scientist than a conventional wizard, showing an almost fanatical curiosity for new technologies, whether magical or from Saito's world.

This scientific drive forms his primary motivation. He feels a profound sense of skepticism toward his society's rigid class structure and seeks to use his inventions to build rather than destroy. His dream is to visit Saito's original world, having been inspired by the advanced technology glimpsed through items like the Zero Fighter plane and Saito's laptop. To this end, he single-handedly designs and constructs the airship Ostland, a testament to his engineering brilliance.

Within the story's narrative, Colbert is first presented as an eccentric but wise teacher. His role expands significantly during the war with Albion, when his past is publicly revealed. After this crisis, he becomes a key supporting character and a consistent "Big Damn Heroes" figure, arriving at critical moments aboard the Ostland to rescue Saito, Louise, and their friends from seemingly inescapable danger.

His key relationships are shaped by his secret history. He shares a complex dynamic with Agnes, the very person whose home he destroyed, creating a tense undercurrent of potential vengeance and eventual, hard-won understanding. His relationship with the fiery Kirche von Zerbst evolves from one of her mild disdain—she felt he was not a "proper" fire mage due to his focus on invention over passion—to a deep romantic connection after witnessing his true capabilities and noble heart.

Throughout the series, Colbert develops from a guilt-ridden hermit of science into a man who has begun to forgive himself and re-engage with the world. His inventions not only serve the plot but also represent his psychological journey: turning flames that once killed into engines that drive airships and generate electricity. His notable abilities are vast. He is considered one of the most powerful mages in the world of Halkeginia, capable of easily defeating elite soldiers and enemy wizards with his fire magic. However, his most remarkable talent lies in his scientific mind, allowing him to synthesize gasoline through alchemy, create alternating and direct current electricity, and reverse-engineer complex technology using only basic magical principles.