Yeon Gaesomun (603–666) is a powerful and controversial military dictator in the waning days of Goguryeo, which is one of the Three Kingdoms of ancient Korea.

Yeon is also remembered for a number of successful resistance in military conflicts with the Tang Dynasty under Emperor Li Shimin and his son Emperor Gaozong.

Their failure against Yeon is the only defeat that Emperor Li Shimin ever suffers on the battlefield.

Traditional Korean histories paint Yeon as a despotic leader, whose cruel policies and disobedience to his monarch lead to the fall of Goguryeo.

However, his achievements in defending Goguryeo against Chinese onslaughts have inspired Korean nationalist historians, most notably the 19th century Korean historian and intellectual Shin Chaeho, to term Yeon the greatest hero in Korean history.

Many Korean scholars today echo Shin and praise Yeon as a soldier-statesman without equal in Korean history, though other scholars strongly disagree.