Historicity
Modern scholars have come to question the existence of at least the first nine emperors (cf. List of Emperors of Japan); and Sujin is the first many agree might have actually existed, in the third or fourth centuries.
Sujin is regarded by historians as a "legendary emperor" and the paucity of material information about him makes difficult any further verification and study. The reign of Emperor Kimmei (509–571), the 29th emperor of Japan according to the traditional order of succession, is the first for which contemporary historiography are able to assign verifiable dates; however, the conventionally accepted names and dates of the early emperors were not to be confirmed as "traditional" until the reign of Emperor Kammu (737–806), the 50th sovereign of the Yamato dynasty.
Sujin-tennō is a Posthumous name assigned by later generations, possibly ascribed during the compilation of the Kojiki.
Read more about this topic: Emperor Sujin