Fidei defensor (Latin meaning defender of the faith) is a title of British monarchs first conferred by Leo X on Henry VIII for his book Assertio septem Sacramentorum, published in 1521 which attacks the doctrines of Luther. At the dissolution of the monasteries the Pope stripped Henry VIII of the title, but Parliament confirmed it in 1544 and it has been used by all British monarchs subsequently, being indicated on British coins as FID. DEF. Research Fidei Defensor