Daijo Tenno (太上天皇)
Daijo Tenno (the Retired Emperor) is an honorary title awarded to an Emperor who handed over the Imperial Throne to his successor. Or, it refers to the person who was awarded the honorary title. It is often abbreviated as Joko.
It is said to have originated from the fact that when a Chinese Emperor stepped down from the throne, he was respectfully called 'Daijoko.'
In addition, Joko who became a priest is called Daijo Hoo (Cloistered Retired Emperor). However, there is no legal class difference between the two and, in the Ritsuryo law system, Daijo Hoo is included in Daijo Tenno.
Daijo Tenno is often called 'In,'
'In' and 'Sangu' (the Empress, the Dowager Empress, the Grand Dowager Empress) are collectively referred to as 'Ingu' and, further including dominant nobilities, temples and shrines, they were collectively termed Ingu oshinke. Because the palace of 'In' was called Sento Imperial Palace, 'Sento' is also used to as a term for Joko.
The first Emperor to become Daijo Tenno was Emperor Jito, who handed over the throne to Emperor Monmu, (though there is an example of Empress Kogyoku, who transferred the throne to her younger brother Emperor Kotoku, but at this time, there was no title of 'Daijo Tenno' and, thereafter, she acceded to the throne again as Empress Saimei) and up until Emperor Kokaku handed over the throne to Emperor Ninko in the late Edo period, there were 62 Joko's in total.
However, they include instances where Emperors thought it was ominous to die while in the reign and arrangements were immediately made to hand over the throne before the demise, with the honorary title of Daijo Tenno being awarded and the Daijo Tenno passing away soon thereafter. Typical are 8 days from transfer of the throne to the demise for Emperor Daigo, 10 days for Emperor Ichijo, and 3 days for Emperor Gosuzaku.
To most Emperors, the titles of Daijo Tenno were awarded soon after transfer of the throne but, because it was not awarded automatically with the transfer, there were cases where the honorary titles were not awarded as was the case with Awaji haitei (the deposed Emperor of Awaji) (Emperor Junnin), who was abdicated in something like a coup, and with Emperor Antoku and Dethroned Emperor Kujo (Emperor Chukyo) whose abdication and enthronement were made obscure. There was a case where, on the occasion of the death of Yoshimitsu ASHIKAGA, the Imperial Court offered to award him the honorary title of Daijo Tenno, but eventually his son Yoshimochi ASHIKAGA refused to accept. In 1817, after Emperor Kokaku handed over the throne to Emperor Ninko to become the Daijo Tenno for the last time, there existed no Daijo Emperor. Because the Imｐerial House Acts after the Meiji period do not admit transfer of the throne, the rule of Daijo Emperor does not exist until the present time.
Insei/Chiten no kimi
In Taiho Ritsuryo (Taiho Code), there was a provision for Joko alongside that for Emperor which made it possible for Joko to incorporate his intent politically by means of inzen (a decree from In) just like Emperor. Joko could also establish institutions such as In no cho (Retired Emperor's Office) and set up organs such as inkurodo (Chamberlain of In no cho), etc.
At the end of the Heian period, Insei (rule by In (= Joko)) based on a father-child relationship with the Emperor began to be conducted instead of Sekkan seiji (regency) based on a mother-child relationship. Many of historically famous Joko's belong to this period.
These Joko's who assumed the reigns of government also belong to those who were referred to as Chiten no kimi (the retired emperor in power) (however, Joko who assumed power is not necessarily a Chiten no kimi.)