Eulji Mundeok was a noted military leader of early 7th century Goguryeo, one of the Three Kingdoms of Korea. Often numbered among the greatest heroes in Korean military history, he defended Goguryeo against the Sui Chinese. His name is often romanized as Ulchi Mundok according to McCune-Reischauer romanization.
A balance of power was maintained between these Three Kingdoms of Korea, until outside influence, namely the much larger Tang Dynasty of China, finally tipped the advantage to Silla. In 589, the Sui Dynasty had reunified China for the first time since the fall of the Han Dynasty over three centuries before. The Sui early on launched several large military campaigns against Goguryeo unwilling to submit to Sui dominance.
Eulji Mundeok (some Korean scholars posit that the Eulji 乙支 in his name is some form of Goguryeo rank or title) was an educated man, skilled in both "mun" (문, 文) political and the "mu" (무, 武) military sciences. He eventually rose to become Prime Minister of Goguryeo.
In the early 7th century, however, the new Sui emperor Yangdi learned of secret Goguryeo correspondence with the Eastern Turkish khanate. Yangdi took a hard stand and demanded the King Yeongyang come and submit personally to Sui or face an "imperial tour of his territories". When the King Yeongyang failed to submit in this fashion, Yangdi prepared for war. He mustered an army of over 1,133,800 troops and more than 2 million auxiliaries and personally led them against Goguryeo in 612. They quickly overran Goguryeo's border defenses, camped on the banks of the Liao River and prepared to bridge it. Eulji Mundeok, commissioned as a Field Marshal, was called upon to assist in the defence of the nation, and prepared his troops to meet the superior Sui forces with a strategy of false retreat, deception and attack.
After the Sui forces crossed the Liao River, a small contingent was sent to attack the Goguryeo city of Liaodong, but Field Marshal Eulji sent Admiral Gang Yi-sik and his forces to meet them there and drove them out. As the rainy season progressed, the Sui forces launched other small probing attacks, but held off from making any large moves before the end of the rainy season.
When the rains stopped, Yangdi moved his forces to the banks of the Yalu River in northwestern Korea and prepared for a major battle. Fighting only small engagements at times and places of his choosing, he drew the Sui forces further and further from their supply centers. A Sui advance force of over 305,000 men was sent to take the city of Pyongyang. After allowing the force to approach the city, Field Marshall Eulji ambushed it. His forces attacked from all sides, driving the Sui troops back in utter confusion. His troops pursued the retreating army, slaughtering them at will; records claim that only 2,700 men of the massive force returned alive to the main Chinese army. This battle, the Battle of Salsu, came known as one of the most glorious military triumphs in Korea's national history. (It was said that Eulji had built a large dam upon the Salsu river which made the waterbed shallow, and as the Sui troops crossed the dam was broken down, releasing a huge current of water upon the unsuspecting troops, thus wiping out nearly the entire fleet with one blow). After the battle, winter began to set in and the Sui forces, short on provisions, were forced to return home.
The Sui Dynasty was beginning to disintegrate and Yangdi decided that he urgently needed to expand his empire in order to regain power, but two more attacks on Goguryeo by Yangdi the following spring met with similar disaster, and eventually internal rebellion in China forced the Sui to abandon their desire for Goguryeo. By 618, the relatively short-lived Sui Dynasty was replaced by the Tang Dynasty. Field Marshal Eulji Mundeok's strategy and leadership had protected Goguryeo from the Chinese expansion to the Korean peninsula.
Eulji Mundeok has been recognized as one of the most famous and greatest figures throughout the Korean history. During the reign of Hyeonjong in the Goryeo period, a shrine of Eulji Mundeok was built near Pyongyang. In the Joseon period, he was one of the most revered figures as well as in the previous period. For instance, Yang Seong-ji, a scholar and high-ranking bureaucrat of Early Joseon, and An Jeog-bok, a Silhak historian of Late Joseon, thought highly of him. Furthermore, Sukjong of Joseon ordered to construct another shrine in honour of Eulji Mundeok in 1680. At the time when Korea was suffering under the yoke of Japanese Imperialism, the assessment of Mundeok may have begun with the Korean historian Sin Chaeho (신채호, 申采浩, 1880-1936), who published a biography of Mundeok in 1908 and held him out as an example of Korea's traditional nationalist spirit Eulji Mundeok is still celebrated as a great Korean hero. One of the most preeminent Korean scholars of the 20th century, Lee Ki-baik, noted that Mundeok's efforts in halting the Sui attempt at conquest stand as one of the earliest examples of Korean attempts to fend of foreign domination. Today a main thoroughfare in downtown Seoul, Euljiro, is named after Eulji Mundeok. The second highest Military Decoration of South Korea, Field Marshal Lord Eulji's Order of Military Merit, is also named in his honour.
Eulji Mundeok's literary work, the Eulji Mundeok Hansi, is one of the oldest surviving poems in Korean literature.