Complex sentence: He is the son of Lucille (Proulx) Mattis and John Mattis (1915--1988), who worked as a merchant mariner and his mother had worked in Army Intelligence in South Africa during the Second World War.
Split into simpler sentences: He is the son of Lucille (Proulx) Mattis and John Mattis (1915--1988), who worked as a merchant mariner. His mother had worked in Army Intelligence in South Africa during the Second World War.