Richard of York, 3rd Duke of York, also named Richard Plantagenet, was a leading English magnate and claimant to the throne during the Wars of the Roses. He was a member of the ruling House of Plantagenet by virtue of being a direct male-line descendant of Edmund of Langley, King Edward III's fourth surviving son. However, it was through his mother, Anne Mortimer, a descendant of Edward III's second surviving son, Lionel of Antwerp, that Richard inherited his strongest claim to the throne, as the opposing House of Lancaster was descended from John of Gaunt, Duke of Lancaster, the third surviving son of Edward III. He also inherited vast estates and served in various offices of state in Ireland, France and England, a country he ultimately governed as Lord Protector due to the mental instability of King Henry VI.

Lord Protector was a title that has been used in British constitutional law for the head of state. It was also a particular title for the British heads of state in respect to the established church. It was sometimes used to refer to holders of other temporary posts; for example, a regent acting for the absent monarch.