Jaesan Jeon is a prominent figure in the world of The God of High School, recognized as a former member of The Six, an elite group of the most powerful Charyeok users in South Korea. He also served as the chairman of the Sixsung Corporation, a massive and influential company. His immense power and status earned him the title of a living National Treasure.

In terms of background, Jaesan was a prodigy in the art of magic and Charyeok. His skill was so exceptional that by the age of thirty-seven, he was officially recognized as an archmage by the National Magician Association. A decade later, at forty-seven, the South Korean government granted him membership in The Six, hoping he would act as a figure who could keep the increasing number of Charyeok users in line. Beyond his official roles, he took on Sin Yunseong as his apprentice after being impressed by the young man's actions, teaching him magic for fifteen years and eventually having him act as his chief secretary and tutor to his grandson.

Jaesan's personality is marked by a blend of old-school values and deep personal pride. Despite his immense prestige, he holds onto a sense of old-style chivalry, viewing the protection of innocents and the maintenance of peace as his duty. His charisma as a corporate leader also made him first among equals within The Six. However, he possesses a complex about his own large size and dislikes when others comment on it. His beliefs about strength are particularly defining; he is a proponent of the idea that people must be born with power and cannot become truly strong through sheer effort alone, a philosophy that placed considerable pressure on his grandson, Jeon Jugok. While he deeply loves Jugok and is proud of him, this belief led him to be coldly pragmatic after Jugok lost a match, asking the victor, Park Ilpyo, to become his student instead. This act was not borne of malice but of his rigid worldview regarding innate talent.

Jaesan's primary motivation throughout the story is rooted in his responsibilities and his family. He is deeply concerned with the rising number of rogue Charyeok users and the growing threat of the organization known as Nox. This concern drives him to action, leading him to establish "Shadow," a secret subsidiary of Sixsung designed to employ or eliminate unsanctioned Charyeok users. On a personal level, his most powerful motivation becomes revenge. When his grandson Jugok is humiliated and later killed in the God of High School tournament by Jegal Taek, Jaesan is consumed by a desire for retribution. His efforts become focused on getting Jegal Taek handed over to him, a promise he pursues relentlessly.

His role in the story is that of a powerful ally and a tragic figure of vengeance. As a member of The Six, he is a key figure on the side trying to maintain order. He is first seen watching his grandson compete, then later mourning his death. His role culminates in the defense of Seoul against the Bishop Sang Mandeok. In a massive display of power, he single-handedly teleports the entire population of the city to safety, transforms hundreds of incoming nuclear missiles into a single bomb using alchemy, and summons a giant meteor to destroy a summoned Nephilim. This act, which he knows will break a magical taboo and lead to his death, represents his final and greatest contribution to the battle.

Key relationships define much of his narrative. The most significant is with his grandson, Jeon Jugok. Their relationship is complex, built on genuine love and pride but strained by Jaesan's demanding belief in innate strength. His relationship with his apprentice, Sin Yunseong, is another important bond, built on decades of training and trust, to the point where Jaesan bequeaths part of his wealth to him. His fellow members of The Six, such as Park Mujin and Seo Hanryang, are his allies and rivals, and his interactions with them, particularly his demand for Jegal Taek, drive key political conflicts in the story.

Jaesan's development is a tragic arc from a respected, if flawed, patriarch to a shattered avenger. He begins as a confident chairman and a member of the powerful Six. The death of his grandson is a turning point that strips away his composure, leaving him focused on revenge. His final battle sees a complete release of his power, not for the sake of the tournament or politics, but for his own duty to protect the city and to attempt to kill his grandson's murderer. His last thoughts are of Jugok, showing that his pride and love for his grandson were his defining traits in the end.

Notable abilities mark Jaesan as one of the world's greatest magicians. He specializes in wizardry and has mastered a Charyeok known simply as The Great Magician, considered the strongest magic-using Charyeok in the world. His techniques include Teleport, with which he can move an entire province's population miles away. He can cast Protector, an immensely strong barrier, and Anti-Teleport, which locks an opponent in a confined space. His most destructive power is Meteor, allowing him to summon a massive meteor from space. He also wields Alchemy, giving him the power to convert and create objects from pre-existing material; his most famous feat was transforming 567 nuclear missiles into a single, magically-imbued super-bomb.