Fidei defensor
Fidei defensor (Defender of the Faith) was a title granted on October 17, 1521 by Pope Leo X to King Henry VIII of England on the basis of Henry's book Assertio Septem Sacramentorum, written with the uncredited assistance of Thomas More, which defended the sacramental nature of marriage and the supremacy of the Pope.The title was a reward for the resistance in England to the new ideas of Martin Luther. When the king broke with Rome the title was revoked by Pope Paul III. The English parliament confirmed the title in 1544 for Anglicanism. Its continued use can be seen as something of an anti-Catholic gesture by the monarchy.
The Latin version of the title, abbreviated to FD, is seen on all current British coinss. It was first placed on coins in 1714.
Recently, Charles, Prince of Wales has said that he would like to recast the title as Defender of Faith (Fiderum defensor), to avoid the appearance of favouring one religion above another.
