Somerset, Edward Seymour, Duke of (1506–1552), an English statesman. The uncle of Edward VI, who became king as a child, Somerset was named protector and was, in effect, head of government, 1547–49. As protector, he played a leading part in the Protestant Reformation in England. He repealed Henry VIII's treason and heresy laws, used mainly for religious persecution. In 1549 he issued and enforced the use of the First Prayer Book of Edward VI (Book of Common Prayer), which contained Protestant doctrine and was written entirely in English. Somerset's actions alienated both religious and political conservatives; he was deposed in 1549 and was later beheaded.