Who is Marquis de Casalduero, Don Ygnacio from Of Love and Other Demons and what is their importance?

The Marquis is the father of Sierva. He is a weak man, who is bossed around and manipulated first by his father and later by his wives. His first wife is miraculously killed by a thunderbolt. This is an example of the novel's magical realism. The Marquis is also tricked into marrying Bernarda, who arranges to have him impregnate her and have their daughter, Sierva.