Kwanggaet'o (375-413) was the nineteenth ruler of Kogury, an ancient northern Korean kingdom. A brave warrior and a great national leader, he was known chiefly for his successful conquest and expansion of Kogury territory.

Son of King Kogugyang (reigned 384-391), Kwanggaet'o was known during his life as Great King Yngnak, which was also his reign title and the first era name adopted by a Korean king. He took by storm (392, 395) the settlements of Piry, recently identified with the Khitan, along the Liao River; to the west, he repulsed the invasions of the Later Yen, established by the Mu-jung tribes of the Hsien-pi, and occupied the Liaotung Peninsula (400, 405, 406). To the northeast, he subjugated the Sukchin people (398); and to the north, he attacked East Puy, extending Kogury's northern border (410).

Kwanggaet'o's southward expansion was equally successful. With the fall of the Chinese commanderies Lolang and Tai-fang, Kogury and the southern kingdom...