King Taejong Muyeol was born with the "sacred bone" rank of seonggol. His father, Kim Yongsu (金龍樹), was a son of Silla's 25th ruler, King Jinji. When King Jinji was overthrown, all royalty from his line, including Kim Yongsu, were deemed unfit to rule over the kingdom. However, as he Yongsu was one of the few remaining seonggols, and married a seonggol princess (King Jinpyeong's daughter Princess Cheonmyeong), their child, Kim Chunhcu, became seonggol and thus had a claim to the throne. Kim Yongsu was a powerful figure in the government. However, he lost all of his power to Kim Baekban, the brother of the king. In order to survive, he had accepted to become a jingol, the rank that was right below seonggol. Therefore, he lost his chance of becoming the king, and so did his child, Kim Chunhcu. Following the death of his aunt, Queen Seondeok, Chunchu was passed over in favor of Jindeok of Silla, the last verifiable seonggol. With her death, all the seonggols were dead, so somebody with the royal blood in the jinggol rank had to succeed the throne. Kim Alcheon (a.k.a. So Alcheon), who was then Sangdaedeung (highest post of government) of Silla was the original favorite to succeed the throne. His father was a seonggol, who married a jingol wife so that his son would not be a seonggol and suffer from the fight for the throne. However, Kim Yushin supported Kim Chunhcu, and Alcheon eventually refused the throne and supported Chunchu's claim. As a result, Kim Chunhcu succeeded the throne as King Muyeol.