King Taejong Muyeol was born with the "sacred bone" rank of
seonggol. His father, Kim Yongsu (), was a son of Silla's 25th ruler,
King Jinji. When King Jinji was overthrown, all royalty from his line, including Kim Yong-su, were deemed unfit to rule over the kingdom. However, as Yong-su was one of the few remaining
seonggols, and married a
seonggol princess (
King Jinpyeong's daughter
Princess Cheonmyeong), their child, Kim Ch'un-ch'u, became
seonggol and thus had a claim to the throne. Kim Yong-su was a powerful figure in the government; however, he lost all of his power to , the brother of the king. In order to survive, he accepted to become a
jingol, the rank that was right below
seonggol, therefore removing the right of becoming the king for him and his son, Kim Ch'un-ch'u. Following the death of his aunt,
Queen Seondeok, Ch'un-ch'u 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.
Alcheon, who then held the title
Sangdaedeung, or highest post of government, of Silla was the original favorite to succeed the throne. His father was a
seonggol, who married a
jingol woman so that his son would not be a
seonggol and suffer from the fight for the throne. However,
Kim Yu-sin supported Kim Ch'un-ch'u, and Alcheon eventually refused the throne and supported Ch'un-ch'u's claim. As a result, Kim Ch'un-ch'u succeeded the throne as King Muyeol. ==Marriage to Kim Yu-sin's sister==