Gaero of Baekje (개로왕) (蓋鹵王) (?-475, 455-475) was the 21st king of Baekje, one of the Three Kingdoms of Korea. He was the eldest son of the 20th king Biyu. He died in battle as Baekje's capital in the present-day Seoul region fell to the northern rival kingdom Goguryeo.
He attempted to strengthen royal control of the aristocracy, by selecting officials from his own Yeo clan, at the expense of the powerful Hae and Jin clans.
In 469, he ordered a surprise attack in which the city of Cheongmongnyeon (청목령, 靑木嶺 ; near modern Gaeseong) was retaken from Goguryeo. In 472, he sent an embassy bearing tribute to Northern Wei requesting support against Goguryeo’s attacks. However, these advances were rebuffed by the Wei court, which tried to avoid war with Goguryeo which had greater military power at the time, while fighting against Southern Dynasties.
In the early 470s, according to the Samguk Sagi, King Jangsu of Goguryeo sent a Buddhist monk named Dorim, who was actually a Goguryeo agent. Dorim used Gaero’s passion for the game of baduk to ingratiate himself, and persuade the king to neglect the country’s defense in favor of public works.
Fall of the capital
In 475, Jangsu launched an attack with 30,000 men and overran Baekje’s defenses in seven days, taking the Han River valley including the capital. Gaero was taken to Achasanseong and slain by two men who had defected to Goguryeo from Baekje. Baekje's ally Shilla sent an army of 10,000, but arrived too late.
He was the last to rule Baekje from its historic heartland in the Han River valley. After his death, Hae Gu, of the suppressed Hae clan, led a bloody revolt.