Osman, whose name is also rendered Osmond and who is often addressed as Old Osman, is the elderly headmaster of the Tristain Academy of Magic, the school at the center of the story. He is portrayed as a white-haired older man of Tristain nationality who has spent many years leading the institution. Not much is revealed about his personal past, but his age and position suggest a long and experienced career as both a noble and a mage, and he is treated with a degree of deference by students and staff alike.

In personality, Osman is outwardly a lecherous old man with a well-known weakness for attractive younger women. He enjoys smoking and frequently makes flirtatious remarks, most often directed at his own secretary, Longueville, who handles much of the daily administration of the academy. A recurring comedic trait is his habit of using his familiar, a small mouse named Motsognir, to spy on Longueville, even going so far as to send the creature to discover the color of her underwear. Beneath this unserious exterior, however, he is shown to have a serious side. He is a capable and responsible authority figure who genuinely cares about the safety and reputation of the school, and he can set aside his foolishness when real danger threatens.

As the headmaster, Osman serves as a supporting figure throughout the main storyline. He presides over the academy and its major events, including the familiar summoning ceremony, oversees faculty and students, and becomes involved when crises affect the school or the kingdom. He is often aware of more than he lets on and occasionally offers guidance or quietly steers events in the background, displaying the shrewdness that underlies his comic demeanor. His relationship with his secretary Longueville is one of his most consistent interactions, as she manages much of the academy's operations while enduring his advances. He also has a natural rapport with his familiar Motsognir, whom he uses for surveillance and small errands, and he interacts with the other teachers and students primarily from his position as their superior.

In terms of development, Osman is largely a static character who provides comedy and institutional authority rather than undergoing a personal transformation. His role shifts only in emphasis: at times he is a source of slapstick humor, and at other moments he demonstrates competence, wisdom, and loyalty to Tristain, especially when the school or its students come under threat. His notable abilities are tied to his status as an experienced mage. The anime itself does not show him casting powerful spells, but the story's magic system ranks mages by how many elemental powers they can combine, and the highest class, known as square mages, is extremely rare, with Osman sometimes counted among the few possible examples of that rank. His most distinctive practical ability is the use of Motsognir for espionage, which he employs for both lecherous purposes and, on occasion, more legitimate observation. Overall, Osman is best understood as the wise but eccentric guardian of the academy, masking genuine competence behind an old man's wandering eyes.