Onjo

Onjo of Baekje
Hangul	온조왕
Hanja	溫祚王
Revised Romanization	Onjo-wang
McCune–Reischauer	Onjo-wang

Monarchs of Korea Baekje

Onjo 18 BCE–28 CE Daru 28–77 Giru 77–128 Gaeru 128–166 Chogo 166–214 Gusu 214–234 Saban 234 Goi 234–286 Chaekgye 286–298 Bunseo 298–304 Biryu 304–344 Gye 344–346 Geunchogo 346–375 Geungusu 375–384 Chimnyu 384–385 Jinsa 385–392 Asin 392–405 Jeonji 405–420 Guisin 420–427 Biyu 427–455 Gaero 455–475 Munju 475–477 Samgeun 477–479 Dongseong 479–501 Muryeong 501–523 Seong 523–554 Wideok 554–598 Hye 598–599 Beop 599–600 Mu 600–641 Uija 641–660

Onjo (?-28, r. 18 BC–AD 28) was the founding monarch of Baekje (백제,百濟), one of the Three Kingdoms of Korea. According to the Samguk Sagi (삼국사기, 三國史記), he was the ancestor of all Baekje kings.

There are a few theories and legends of Onjo's parentage. One is that he was the third son of King Dongmyeong (Jumong), the founder of the northern Korean kingdom Goguryeo. He was the younger brother of Yuri, who became Goguryeo's second king, and younger brother of Biryu who built small state in Michuhol.

The second theory is that he is the son of Wutae, his mother's first husband. A third legend says that his older brother Biryu was his mother's son with Wutae but Onjo was born after the second marriage with King Dongmyeong.

Dongmyeong had three sons: Yuri, Biryu, and Onjo. When Yuri, born from Dongmyeong's previous wife in Dongbuyeo, came to Goguryeo and became the heir to the throne, Biryu and Onjo moved south to found their own kingdoms. According to the Samguk Yusa, Biryu founded his kingdom in Michuhol (미추홀/彌鄒忽), but his didn't last long. Biryu's people joined Sipje after Biryu's death and Onjo renamed it to Baekje. After that, the capital city of Baekje was moved southward from Habuk Wiryeseong because the Malgal were located at the North and Nangnang was located to the East. Both capital cities correspond to land within current Seoul. In 3 BC and 8 BC, the Malgal tribes attacked from the north, and both times, Onjo directly led his armies and won victories over the invaders. In 5 BC, Onjo moved the capital city to a more defensible location south of the Han River, renaming it Hanam Wiryeseong, and sent a messenger to the king of the Mahan confederacy telling him of the recent action.

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