Gwanggaeto, The Great Conqueror

Goguryeo, at the time of the protagonist's birth, is no longer as powerful as it used to be. Prior to his birth, his grandfather, King Gogugwon was killed by the Baekje forces led by King Geunchogo. When his uncle King Sosurim died without an heir, his father King Gogugyang rose to the throne of Goguryeo. At the same time, they were also under attack by the Later Yan forces, led by none other than the Emperor of Later Yan himself, Murong Chui. After his father's death, he rises to the throne and vows to restore Goguryeo to its former glory. His struggle would later form the basis of a popular Korean legend. He would regain land lost to Baekjae, and he will defeat many other smaller kingdoms in the process. Near the end of the story, he manages to obliterate Later Yan and later subjugated her as a sister state.