Margaret Plantagenet, Countess of Salisbury, was the only surviving daughter of George Plantagenet, Duke of Clarence, a brother of Kings Edward IV and Richard III, by his wife Isabel Neville. As a result of her marriage to Richard Pole, she was also known as Margaret Pole. One of the few members of the House of Plantagenet to have survived the Wars of the Roses, she was executed in 1541 at the command of King Henry VIII, the second monarch of the House of Tudor, who was the son of her first cousin, Elizabeth of York. Pope Leo XIII beatified her as a martyr for the Catholic Church on 29 December 1886. One of her sons, Reginald Pole, was the last Catholic Archbishop of Canterbury.

George Plantagenet, Duke of Clarence, was the sixth child and third surviving son of Richard Plantagenet, 3rd Duke of York, and Cecily Neville, and the brother of English kings Edward IV and Richard III. He played an important role in the dynastic struggle between rival factions of the Plantagenets now known as the Wars of the Roses.