Dukes in the United Kingdom
Duke, in the United Kingdom, is the highest-ranking hereditary title in all four peerages of the British Isles. A duke thus outranks all other holders of titles of nobility (marquess, earl, viscount and baron).
History of the British peerage
At first, earls and barons were the only ranks in the peerage. The other ranks of the Peerage developed in the fourteenth and fifteenth century. In 1337, Edward, the Black Prince was created Duke of Cornwall, taking precedence over all earls. Dukedoms were reserved for members of the Royal Family until 1387, when Robert de Vere, 9th Earl of Oxford, the favourite of Richard II, was created Duke of Ireland for life. De Vere had previously been created Marquess of Dublin for life, making him the first person to hold a dignity of such a rank between Dukes and Earls. Subsequent marquessates were created rarely; the Marquess of Winchester, whose dignity was created in 1551, is the only English marquess without a dukedom. The rank of viscount was introduced from Europe in 1440, when John, Baron Beaumont, was created Viscount Beaumont, with precedence between earls and barons.