Emperor Go-Daigo
Go-Daigo became emperor in 1318 when he was 30 years old.  This was not usual for the time.  Usually, small boys were made emperor.  When they became adult men, they went to religious communities for men, where they would set up a government and rule even though they stayed in the monastery.  A new boy from the imperial family was put on the throne.  This system, with a boy on the throne in public and a "former" emperor ruling from a monastery, was called cloistered rule or insei.