King Onjo was a founder of the Baekje Dynasty who ruled from 18 BCE to 28 CE. Onjo was Dongmyeong of Goguryeo’s youngest son. Dongmyeong was a legendary founder of the Goguryeo Dynasty who ruled from 58 BCE to 19 BCE.
When Dongmyeong fled Northern Buyeo to start his own kingdom, he left behind his first wife and son, Yuri. Dongmyeong later married the second daughter to an aging king. She bore him two sons, Biryu and Onjo. Shortly before Dongmyeong’s death, his first son from Norther Buyeo came to Goguryeo court to seek his father. Yuri was named the Crown Prince and the throne passed to him after Dongmyeong’s death.
Biryu and Onjo remembered back to their father’s trouble in Northern Buyeo. They had no intention of creating tension with their half-brother. Rather than being seen as challengers for the throne, Biryu and Onjo decided to leave Goguryeo to start their own kingdom in the south. They took ten retainers and many followers on their journey.
The group soon arrived at Han Mountain and climbed the peak to look over the land. They saw the Han River to the north, high mountains to the east, a sea to the west, and fertile wetlands to the south. Biryu and Onjo’s retainers argued to establish their new kingdom just below the Han River as they saw that the land possessed everything they needed. However, Biryu had his heart set on a land closer to the sea and departed with his followers. The ten retainers decided to stay with Onjo to establish a new capital called Wirye and called the country Sipche.
Biryu continued until he arrived at Michuhol. The land was not what he had expected, and it was inhospitable for living. In regret, he made his way to back to his brother with his followers. Biryu died shortly after and his followers settle in Sipche.
As King Onjo was a descendent of Buyeo, he used Buyeo as his family name. He also changed the name of the country to Baekje.
King Onjo’s first trouble came in his eighth year on the throne. On a cold spring day, three thousand Malgal invaders came down south to surround Wirye Fortress. King Onjo decided to wait out the invaders by refusing to meet them in battle. He waited patiently until Malgal troops started to run out of provisions and were withdrawing. King Onjo sent troops after the hungry and exhausted Malgal troops and easily defeated them. However, this was just the beginning of their difficult relationship.
In his thirteen year on the throne, King Onjo decided to move the capital further south to take relief of invading Malgals. With constant danger from his enemies, King Onjo ordered several fortresses built to protect his kingdom.
King Onjo soon realized that the only way to protect this people and his kingdom was to expand his territory and built up this military. He needed to destroy Mahan and Jinhan in order to have peace. King Onjo continued to build fortresses and met his enemies in the battlefield. Declining Mahan eventually surrendered to Baekje and King Onjo took the people of Mahan as his own. While there were several rebellions, King Onjo and his troops easily defeated them.
After 46 years on the throne, King Onjo died in early spring and passed the throne to his son, Daru. King Onjo had created a strong dynasty that would nearly 700 years.