The Emperor: Owner of the Mask (Korean: 군주-가면의 주인; RR: Gunju – Gamyeonui juin; lit. Ruler – Master of the Mask) is a South Korean television series starring Yoo Seung-ho, Kim So-hyun, Kim Myung-soo, Yoon So-hee, Heo Joon-ho and Park Chul-min.
During the Joseon Dynasty, the long-awaited son of King Yi Yoon is born, but in exchange for its life, the king will hand over the power of the Bureau of Water Supply to the secret society “Pyunsoo Group” that controls the government. The king covers the Crown Prince’s face with a mask and raises him secretly in order to protect him from the Pyunsoo Group.
Sixteen years later, Crown Prince Yi Sun, who grew up as a respectable young man, removes his mask and left the palace secretly to go to the town to find out why he has been masked since he was born. The purpose is to meet scholar Master Woo Bo who is the only person who knows why.
Crown Prince Lee Sun then meets high-ranking official’s daughter Lady Han Ga-eun and a young man who has the same name as himself, Lee Sun, and deepens friendship with them.
After some time, the secret society Pyunsoo Group assassinates King Yi Yoon but Crown Prince Yi Sun escaped. The Pyunsoo Group put a fake king on the throne and controls this king and the whole Imperial Court by using a suspicious drug with poisonous properties. Having witnessed the people’s suffering, the Crown Prince decides to devote himself to fight the Pyunsoo Group and reclaim his throne.
- Yoo Seung-ho as Crown Prince Yi Sun, the real Crown Prince of Joseon and also known as the Chief Peddler.
- Kim So-hyun as Lady Han Ga-eun,daughter of Deputy Magistrate Han, one of the students of Master Woo Bo and childhood friend of commoner Yi Sun. She has wide knowledge of medicinal herbs.
- Kim Myung-soo as Commoner Yi-sun, initially worked as a water deliverer at the Bureau of Water Supply, student of Master Woo Bo and a childhood friend of Lady Ga Eun. He was planted as a fake king by Pyeon-soo group and this slowly gave birth to his greed and desire to become the true king of Joseon in order to earn Ga-eun’s feelings, as partially driven by his jealousy towards Crown Prince Yi Sun and the manipulation of Kim Dae-mok.
- Yoon So-hee as Kim Hwa-gun, granddaughter of Pyunsoo Group leader Dae-mok and head of all the merchants in Joseon. She fell in love with the Crown Prince at first sight. And, remained loyal towards the Crown Prince till the end.
- Heo Joon-ho as Kim Dae-mok, head of the secret society “Pyunsoo Group.” He controls King Yi Yoon and the imperial court by using a mysterious drug with poisonous properties. He forgives no one when they betray Pyunsoo Group, and he even went as far as to murder his own granddaughter for betraying him and showing loyalty to the Crown Prince.
- Park Chul-min as Master Woo-bo, a scholar in medicine and well-versed in Western knowledge.
- Kim Byung-chul as Kim Woo-jae. He is the only son of Dae-mok and also the leader of Pyungsoohwe group. He is the father of Hwa-gun. He is foolish and often despised by his father Dae-mok, but he is very caring towards his daughter.
- Kim Jong-soo as Joo Jin-myung
- Do Yong-goo as Choi Sung-gi
- Jung Kyu-soo as Heo Yoo-gun
- Kim Young-woong as Jo Tae-ho. The head of Water Bureau.
- Kim Seo-kyung as Gon, the loyal bodyguard of Lady Hwa-gun. Later, it was revealed that he was in love with his Lady, Hwa-gun. Out of love for Hwa-gun, he granted her last wish before her death by switching his allegiance to the Crown Prince and protects him from Dae-mok.