King Taejo of Joseon was the founder and the first king of Korea's Yi Dynasty. Born in a Chinese scholar's family, Yi joined the Goryeo army and rose through the ranks. He seized the throne of Korea with the help of China.
During the beginning of the eleventh century Mongol forces had advanced into China and the Korean peninsula, and by the year 1238 Goryeo was fully under Mongol domination and would remain so for the next full century. The Ming Dynasty in China had grown extremely powerful during the 14th century, however, and began to beat back the Mongol armies, so that by the 1350s Goryeo had regained its independence, although China garrisoned a large number of troops in the north-east of Goryeo, effectively occupying part of the country.
General Yi Seonggae had grown in power and respect during the late 1370s and early 1380s, and many at the court plotted to dethrone the then-King U and replace him with General Yi. In 1388, General Yi Seonggae was ordered to use his armies to push the Ming armies out of the Korean peninsula. The general, however, was no fool. He realised the strength of the Ming forces when he came into contact with them at the Yalu River, and made a momentous decision that would alter the course of Korean history. Knowing of the support he enjoyed both from high-ranking government officials and the general populace, he decided to return to the capital, Kaesong, and secure control of the government instead of possibly destroying his army by attacking the Chinese.
Yi marched his army into the capital, defeated the forces loyal to the king (led by General Choi Yong) and removed the government, but did not ascend the throne right away. King Gongyang and his family were sent into exile in 1392 (where they would later be secretly murdered), but the renowned scholar, poet and statesman Chong, Mong-Chu faithfully supported the king, leading the opposition to Yi’s claim to the throne. Chong was revered throughout Goryeo, even by Yi himself, but he was seen to be an obstacle and as such had to be removed. Yi threw a party for him and afterward, on his way home, Chong was murdered by five men on the Sonjukkyo Bridge in Kaesong. This bridge has now become a national monument, and a brown spot on one of the stones is said to be a bloodstain of his which turns red when it rains.
The 474-year-old Goryeo Dynasty effectively ended with the exile of King Gongyang and the death of Chong, Mong-Chu, and was followed by the Yi Dynasty. General Yi took the name "Taejo" on ascending to the throne.