Soga no Zentoko (蘇我善徳)
SOGA no Zentoko (year of birth and death unknown) was a person who was regarded as the eldest son of SOGA no Umako. He was the first official (tera no tsukasa) of Asuka-dera Temple (Hoko-ji Temple).
The volume 22 of "Chronicles of Japan" states '推古四年(596年)冬十一月 法興寺造竟 則以大臣男善徳臣拝寺司 是日恵慈 恵聡二僧 始住於法興寺(冬十一月、法興寺 造り竟(おは)りぬ.則(すなは)ち大臣の男 善徳臣を以て寺司に拝す。是の日に、恵慈、恵聡、二の僧、始めて法興寺に住り。)'
The age of SOGA no Emishi who appeared in the article of the volume 22 in 610 of "Nihonshoki" (Chronicles of Japan) was 25 according to "Fuso Ryakki" (A Brief History of Japan). Because the age of Emishi in 596 was 11, Zentoko is assumed to have been the elder brother of Emishi.
Others
It is not an academic thesis, but there is an opinion that Prince Shotoku, Soga no Iruka was the same person as Soga no Zentoku.