His real name is Yi Seon, Crown Prince Sado. Although he is the heir to the throne, he was driven to madness by his father's extreme educational fervor and pressure from a young age. He suffers from a compulsive disorder where he burns several sets of clothes before choosing the cleanest one to wear. He frequently experiences severe seizures and brutally massacres any soldiers who show him the slightest disrespect.

The historical King Yeongjo. While history remembers him as a brilliant and politically savvy king, he is an utter failure as a father. He forced his late-born son to study classics from the age of three and made him attend cabinet meetings with government officials. If the boy fell short of expectations or played even a little, he would scold him in front of everyone. Nowadays, he either ignores him entirely or asks him questions only to wash his ears out as if he heard something filthy. He even forced Yi Seon to perform Seokgo-daeje (kneeling on the ground in repentance) for ten days in the dead of winter right after the prince had recovered from an illness.