Complex sentence: Gérard de Villiers (8 December 1929--31 October 2013) was a French writer, journalist and publisher whose "SAS" series of spy novels have been major bestsellers.
Split into simpler sentences: Gérard de Villiers (8 December 1929--31 October 2013) was a French writer, journalist and publisher. His "SAS" series of spy novels have been major bestsellers.