Emperor Go-Komatsu (後小松天皇, Go-Komatsu Tennō, (August 1, 1377 - December 1, 1433) was the sixth of the pretenders to the Northern Court of Japan from May 24, 1382 to October 21, 1392, and then the 100th Emperor of Japan from that date to October 5, 1412.
His personal name was Motohito (幹仁). His posthumous name was given to him in memory of Emperor Kōkō, who was also called Komatsu (the prefix Go-, 後, can be translated as "later", so this gives "Later Emperor Komatsu").
He received this name because both brought the throne back to their lineage: in the case of Go-Komatsu, by defeating his rivals in the Southern Court, and in the case of Emperor Kōkō, by succeeding Emperor Yōzei, grandson of his older brother.
Go-Komatsu was the eldest son of his predecessor Go-En'yū. His mother was Tsūyōmonin no Itsuko (通陽門院厳子), daughter of the imperial seal keeper Kimitada Sanjō (三条公忠, Sanjō Kimitada ).
He had several children, among them his heir Emperor Shōkō, and the Zen monk Ikkyū Sōjun (illegitimate, from a daughter of a vassal of the Southern Court).
He also adopted Prince Hikohito (grandson of the northern suitor Sukō, and future emperor Go-Hanazono).
Go-Komatsu is raised in the house of Sukenori Hino (日野西資教, Hino Sukenori). He became emperor of the north when his father Go-En'yū abdicated.
The latter then became retired emperor, with the help of the shogun Yoshimitsu Ashikaga.
In 1392, following the reunification of the two northern and southern courts, the southern emperor Go-Kameyama returned the three sacred treasures, putting an end to the southern court, and making Go-Komatsu the legitimate emperor of Japan, on October 21, 1392, on the condition that the throne would alternate between the two lineages every ten years.
However, the agreement was not respected. Go-Komatsu did not abdicate until 1412, so it was his own son who then ascended the throne as Emperor Shōkō, and all subsequent emperors descended from the Northern line.
Until 1911, therefore, the emperors of the Northern Court were considered the legitimate emperors, and the Southern Court as illegitimate.
However, a government decision changed this state of affairs, and it is now the Southern Court that is considered legitimate, having been in possession of the Imperial Treasury of Japan.
Therefore, Go-Komatsu is not considered legitimate for the first ten years of his reign.