Kim ChunChu (actor Yoo Seung-Ho) later became King Muyeol of Shilla. Chunchu is the final weapon; he's a character who appears to be clueless at first and causes trouble for Deokman, but he's actually quite prodigious. He'll begin seesawing between Deokman and Lady Mishil in order to be recognized and up his worth.
King Taejong Muyeol (602 – 661, Birth name: Kim Chunchu), was the 29th monarch of the southern Korean kingdom of Shilla(Sinra) and ruled from 654 to 661. He is credited for leading the unification of the Three Kingdoms of Korea.
King Taejong Muyeol was born with "sacred blood." He was born with the rank of seonggol. His father, Kim YongSu, was the son of Silla's 25th ruler, King Jinji. Kim YongSu was one of the few remaining seonggols, and married a princess (Princess Cheonnmyong) who was a seonggol as well, their child, Kim ChunChu, was seonggol by blood. When King Jinji was overthrown, all royalty from his line were deemed unfit to rule over the kingdom. Thus, Kim ChunChu, because his grandfather was overthrown, was considered jingol, the rank that was right below seonggol.