Complex sentence: Opicinus de Canistris (1296--1353) was an Italian priest, writer and artist who generated a number of unusual writings and diagrams, autobiographical in origin, which provide the majority of information about his life.
Split into simpler sentences: Opicinus de Canistris was an Italian priest, writer and artist. Opicinus's drawings and writings are autobiographic and provide the majority of information about his life.