Complex sentence: He is the grandson of the author of a book entitled "A Commentary on" I believed in "", which was was the first Turkish Islamic book written in the Latin alphabet at the early period of the Republican period of Turkey.
Split into simpler sentences: He is the grandson of the author of a book entitled "A Commentary on" I believed in "". The book was the first Turkish Islamic book written in the Latin alphabet at the early period of the Republican period of Turkey.