Tenji

was a king of the Land of Sō, and lover of Kaguya Ōtsutsuki, as well as the father of Hagoromo Ōtsutsuki and Hamura Ōtsutsuki.

Background
Tenji has lived millennium ago before start of the main story. At some point, he became the king of the Land of Sō. His land was in war with Land of Ko. Later, he met Kaguya, and fell in love with her, she later became pregnant with him, and bore him twin sons.