King Taejo(dae) was the sixth monarch of Goguryeo, the northernmost of the Three Kingdoms of Korea. Under his reign, the young state expanded its territory and developed into a centrally ruled kingdom. His 93-year reign is thought to be the third longest of any monarch in the world, although this is disputed.

During the first year of his reign, he centralized the kingdom by turning the five clans into five provinces ruled by a governor from that clan, who were under the direct control of the king. He thereby firmly established royal control of the military, economy, and politics.

Upon centralizing, Goguryeo might have been unable to harness enough resources from the region to feed its population and thus, following historical pastoralist tendencies, would have sought to raid and exploit neighboring societies for their land and resources. Aggressive military activities may have also aided expansion, allowing Goguryeo to exact tribute from their tribal neighbors and dominate them politically and economically.

He fought on various occasions with China's Han Dynasty and disrupted trade between Lelang and Han. In 55, he ordered the construction of a fortress in the Liaodong Commandery. He attacked Chinese border regions in 105, 111, and 118. In 122, Taejo allied with the Mahan confederacy of central Korea and the neighboring Yemaek tribe to attack Liaodong, greatly expanding the realm of Goguryeo. He launched another major attack in 146.