Prince Yeonsan a.k.a King Yeonsan the Terrible (Hanja: 燕山君; Born: 24 October 1476 – Killed: 20 November 1506, Reigned: 1494–1506), born Yi Yung (이융/李㦕), was the 10th king of Korea's Joseon Dynasty. He was the eldest son of Seongjong by his second wife, Lady Yoon. He is often considered the worst tyrant in Joseon Dynasty, notorious for launching two bloody purges of the seonbi elite. He also seized a thousand women from the provinces to serve as palace entertainers, and appropriated the Seonggyungwan hall of study as a personal pleasure ground. Because he was overthrown, King Yeonsan did not receive a temple name - otherwise given his courtesy name of King Heoncheon Hongdo Gyeongmun Wimu the Great (헌천홍도경문위무대왕/憲天弘道經文緯武大王).
Deposed Queen Yoon, formally known as Queen Jeheon, served Prince Yeonsan's father, Seongjong, as a concubine until the death of Queen Gonghye, Seongjong's first wife. With no royal heir, the king was urged by counselors to take a second wife to secure the royal succession. Lady Yoon was chosen for her beauty, and was formally married in 1476. Several months later, she gave birth to her first son, Yi Yung, later to become Prince Yeonsan. The new queen proved to be temperamental and highly jealous of Seongjong's concubines living inside the palace, even poisoning one in 1477. In 1479, she physically struck the king one night, leaving scratch marks. Despite efforts to conceal the injury, Seongjong's mother, Queen Dowager In-soo, discovered the truth and ordered Lady Yoon, now known as the Deposed Queen Yoon, into exile. After several popular attempts to restore the deposed Queen to her position at court, government officials petitioned that she be poisoned, and she was.
The Crown Prince grew up and succeeded Seongjong in 1494. During his early reign, he was a wise and able administrator who strengthened the national defense and aided poor people. He also showed signs of violent side when he killed Jo Sa-seo, one of his tutors, soon after becoming the king. He eventually learned what happened to his biological mother and tried to restore his mother's title and position posthumously.
When the government officials belonging to political faction called Sarim opposed his efforts on the account of Seongjong's will, he was displeased and looked for ways to eliminate them. In 1498, Kim Il-son, a disciple of Kim Jong-jik, included a paragraph in the royal record that was critical of King Sejo's usurpation of throne in 1455. Kim Il-son and other followers of Kim Jong-jik were accused of treason by a rival faction, which gave King Yeonsan enough cause to order execution of many Sarim officials and mutilation of Kim Jong-jik's remains. This is called the Moo-oh Literati Purge of 1498 (무오사화/戊午士禍).
In 1504, Im Sa-hong revealed to King Yeonsan details of his mother's death and showed blood-stained piece of clothing, which was allegedly blood vomited by her after drinking poison. On March 20, 1504, he beat to death two of his father's concubines, for their responsibility for his mother's death. His grandmother, Queen Dowager In-soo, died when she was pushed by King Yeonsan after one of altercations. He executed many government officials who supported the execution of his mother, now posthumously known as Queen Jeheon, and ordered the grave of Han Myeong-hoi to be opened and the head cut off the corpse. This is known as the Gapja Literati Purge of 1504 (갑자사화/甲子士禍).
He also closed Seonggyungwan, the royal university, and converted it to his pleasure grounds, for which young girls and horses were gathered from the whole Korean Peninsula. He demolished a large residential area and evicted many residents to build hunting grounds. He also forced people into involuntary labor to build another pleasure ground. Many commoners mocked and insulted the king with posters written in hangul. This provoked the anger of King Yeonsan, and he banned the use of hangul.
When ministers protested his actions, he abolished the Office of Censors (whose function was to criticize inappropriate actions or policies of the king) and Hongmungwan (library and research center that advised the king with Confucian teachings). He ordered his ministers to wear a sign that read: "A mouth is a door that brings in disaster; a tongue is a sword that cuts off a head. A body will be in peace as long as its mouth is closed and its tongue is deep within." (口是禍之門 舌是斬身刀 閉口深藏舌 安身處處牢). When the chief eunuch Kim Cheo-sun, who served three kings, entreated King Yeonsan to change his ways, the latter killed him by shooting arrows and personally cutting off his limbs, and punished his relatives down to the 7th degree. When King Yeonsan asked the royal secretaries whether such punishment was appropriate, they didn't dare to say otherwise. He also exiled a minister of rites for spilling a drink that he had poured. Many people were afraid of his despotic rule and their voices were quelled, in stark contrast to the liberal era of his father.
In 1506, the 12th year of King Yeonsan, a group of officials - notably Park Won-jong, Seong Hui-an, Yoo Soon-jeong and Hong Gyeong-ju - plotted against the despotic ruler. They launched their coup on 2 September 1506, deposing the king and replacing him with his half-brother, Grand Prince Jinseong (later King Jungjong). The king was demoted to prince, and sent into exile, where he killed the same year. Consort Jang Nok-su was regarded as the 'femme fatale' that encouraged King Yeonsan's misrule and was beheaded. King Yeonsan's young sons: Deposed Prince Successor Yi Hwang and Grand Prince Changnyeong were killed as well. The whereabouts of his daughter, Princess Hwisin is unknown.
King Yeonsan the Terrible is buried at Banghak 3-dong san 77-beonji, Seoul Dobong-gu in prior to coup d'etat which was initiated by King Jungjong's loyalists. King Yeonsan's consort, Deposed Queen Geochang of Shin Clan died 31 years later and buried beside her husband.