藤原定家
He is a specialist in medieval Japanese literature, and his particular known for his work on the history of "waka" of the classical and medieval periods. His notable works include "Shinkokin Wakashū Zenhyōshaku" (新古今和歌集全評釈) and "Fujiwara no Teika to Sono Jidai" (藤原定家とその時代).