Masayasu Hosaka (born 1939) is a Japanese nonfiction writer and historian specializing in the Shōwa era. A graduate of Doshisha University, he is widely recognized for his meticulous documentary research and extensive interviews, which have made him one of Japan's leading interpreters of modern history. His work explores politics, the military, the Imperial family, and key figures of the twentieth century through a rigorous, evidence-based approach. His best-known book, "Emperor Shōwa," offers a comprehensive portrait of Emperor Hirohito, drawing on a vast body of historical sources to illuminate both the emperor's life and the broader history of modern Japan.