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).
Peerages in the United Kingdom
The modern peerage system is a vestige of the custom of English kings in the 12th and 13th centuries; in the late 14th century, this right (or "title") began to be granted by decree, and titles also became inherited with the rest of an estate under the system of primogeniture. Non-hereditary positions began to be created again in 1867 for Law Lords, and 1958 generally.