Dae-su. In episode 1, he disguises himself as a junior eunuch and sneaks into the courtyard where his father was imprisoned in a rice chest. With the help of Dae-su and Song-yeon, he manages to see him and obey his father's last wish. The friendship that developed as a result would last the entire series. The plot then fast-forwards ten years, when San is an adult. San is a filial child who loved his father unconditionally despite the opposition, and never denied his father's innocence, which caused him to get into trouble several times. He also never bore a grudge against King Yeongjo, his grandfather, despite Yeongjo's sometimes unfair and harsh treatment towards him. San loved his grandfather deeply. Loyal to his subjects and people, he hates it when someone risks their own life for his, and always tries to protect them instead. While he is still Crown Prince, he falls in love with Song-yeon who became his source of comfort and warmth. Later, when he becomes King, Song-yeon is finally made his concubine. Although San tries to hide it, he never liked the other concubines his mother brought in and hardly ever spent time with them, only doing so once in a while out of a sense of duty as a King, a fact which he is bitter about. San likes practicing martial arts with the Royal Guards and traveling incognito in order to feel the experience of the people. When doing so, he adopts the pseudonym Yi Mu-duk. He suffered severe pain and heartbreak when Song-yeon passes away. While he gravely misses and thinks of her every day, he continued to keep his promise to her that he will withstand everything and be a good King. He is implied to be together with Song-yeon again in their afterlife, where he is finally at peace and happy to spend the rest of eternity with the woman he loves. Titles: Yi San, Wangseson Jeoha (His Royal Highness the Grand Heir→왕세손 저하), Jusang Jeonha (His Majesty the King→주상 전하) Pseudonym: Yi(Ga) Mu-duk (Mu-duk of the Yi clan→이(가) 무덕) Seong Song-yeon/Seong Ui-bin (played by Han Ji-min and Lee Han-na) King Jeongjo's love interest. She is the daughter of a skilled palace artist and thus has a fondness for art. Orphaned at a young age with a baby brother to take care of, she was taken in by a relative who helped her