Complex sentence: The Population Research Institute was founded in 1989 by Paul Marx (1920--2010), a family sociologist, Catholic priest and Benedictine monk who had been the founder of Human Life International, too.
Split into simpler sentences: The Population Research Institute was founded in 1989 by Paul Marx (1920--2010), a family sociologist, Catholic priest and Benedictine monk. He had been the founder of Human Life International, too.