Catherine de' Medici
Her marriage to the second son of Francis I of France was arranged for her when she thirteen. The death of her elder brother in law and then her father in law saw her emerge as the Queen to Henri II of France in 1547. Her husband died in 1559 and her son became Francis II of France. Her son's marriage to Mary Stuart meant that power resided in the hands of Mary Stuart's uncles until the death of the king in 1560. Catherine then became regent to her second son who was ten years old at the time. Catherine was to play a delicate ballancing game between Catholic and Protestant during this time.
Catherine de' Medici is remembered as a practitioner of the principles of Machiavelli. She was ruthless and devious when necessary, and always put her sons hold on the crown of France first.