The intelligent leader of the trio. He is a handsome man among handsome men, characterized by shoulder-length curly brown hair with grey highlights. He possesses strong leadership skills as the head of the Taehak Trio. He often wears a sky-blue hanbok. A Taehak student who, along with Yeon Gae-mun and Dae Jo-yeong, is part of the trio. As a child of nobility with outstanding skills, he receives the trust and admiration of all Taehak students. Disliking Ondal for his commoner origins, he is plotting a conspiracy to eliminate the royal son-in-law. Currently, he is attempting to humiliate him.

He hangs out with Go Jin-pyo and Yeon Gae-mun. He is highly skilled in martial arts. He is a handsome man with short black hair and black eyes. He often wears a blue hanbok.

The tallest among the Taehak Trio. Yeon Gae-mun is an excellent writer. However, he subtly shows signs of potentially taking Ondal's side. He wears his waist-length long hair loosely tied. A handsome man with black hair and black eyes. He often wears a coral-toned hanbok.

The royal son-in-law of Goguryeo (brought from the future by Seol Min-seok). A handsome(?) man with short brown hair. He mainly wears a lime-green hanbok.

The princess of Goguryeo who traveled through time to find a husband. After choosing Ondal, whom she fell in love with at first sight, as her husband, she works hard to help him be recognized as the royal son-in-law. She wants to help whenever Ondal falls into a trap, but she cannot easily step forward due to her status as a princess. A beautiful(?) woman with long purple hair and black eyes. She mainly wears ornate and beautiful dresses.

A great scholar of Goguryeo. He puts in a lot of effort to make Ondal a proper royal son-in-law. He has short dark brown hair, black eyes, and wears glasses. He mainly wears a sky-blue hanbok. All Taehak students call him "Dr. Seol" or "Master Seol."

A monster who seems to possess the combined skills of the entire trio. Short black hair and black eyes. He mainly wears a grey hanbok. His face is just average.