His real name is Yi Seon, the Crown Prince Sado. Although he is the heir to the throne, he went mad due to the intense educational pressure imposed by his father from a very young age. He suffers from a clothing phobia, burning several sets of clothes before finally putting on the cleanest one. He frequently experiences severe seizures and brutally massacres soldiers who he perceives as looking down on him.

The famous King Yeongjo from history. While historically known as a brilliant and politically savvy king, he is a failure as a father. He forced his late-born son to study from the age of three and dragged him into cabinet meetings. If the boy fell even slightly short of expectations or played, he would scold him in front of everyone. Nowadays, he either ignores him entirely or cleans his ears with water as if he heard something foul after asking the prince a question. He even forced Yi Seon to perform a 'Seokgo-daeje' (kneeling on stone) in the dead of winter for ten days right after the prince recovered from an illness.