Sarah Churchill, Duchess of Marlborough
Sir John Jennings KB (died August 1642) of Halywell (later Holywell) House, St Albans, was an English aristocrat and politician who sat in the House of Commons at various times between 1628 and 1642. He is now chiefly remembered as the grandfather of Sarah Churchill, Duchess of Marlborough, and of her nemesis Abigail Masham. He is also notable for the extraordinary number of children he fathered, all from one marriage.