King Gogukyang was the brother of King Sosurim and the father of King Gwanggaeto. Sosurim and Gwanggaeto were distinguished rulers of Goguryeo. The achievements of these two kings, especially King Gwanggaeto, were so great that King Gogukyang is rather overshadowed and he is more commonly known as the father of Gwanggaeto.

When King Sosurim died without an heir in the year 384, his younger brother came to the throne to become the 18th ruler, King Gogukyang. Based on the well-formed state systems established by his predecessor inside the nation, the king actively engaged in outward military expeditions. For instance, the king sent 40-thousand troops to attack the Chinese state of Later Yan in the Liaodong Peninsula in 385, the second year of his reign. The strong Goguryeo forces occupied the Liaodong and Xuantu regions and took 10-thousand prisoners. Historical records indicate that Later Yan was simply no match for Goguryeo, reflecting that the king of Goguryeo was highly aggressive against Later Yan. But Goguryeo lost those two regions to the Chinese state again the following year.

While dealing with the Chinese forces in the west, the king also attacked the southwestern Korean kingdom of Baekje in 386 to expand his territory further south. Baekje returned the attacks a few years later, with the two kingdoms waging fierce battles. King Gogukyang probably had a grudge against Baekje, as the enemy state killed his father, King Gogukwon, who was hit by an arrow and died during a battle with Baekje. The king actually devoted much of his energy to attacking the neighboring state. To keep Baekje in check, the king established a friendly relationship with another Korean kingdom of Silla in the southeastern part of the Korean Peninsula. He even received the Silla king’s nephew as a hostage. In this way, the balance of power among the three kingdoms began to shift during the reign of King Gogukyang, as Goguryeo assaulted Baekje, while making an alliance with Silla. By confronting Later Yan in the west and Baekje in the south, Goguryeo was able to expand its national power.

Domestically, the king further promoted Buddhism to seek cultural development. He also built a national temple and renovated the ancestral shrine to enhance national dignity.

The king died in 391, after a seven year reign. He was succeeded by his son, Dam-deok, who later became the famous King Gwanggaeto the Great.