Duke of Somerset, from the county of Somerset, is a hereditary title that has been created five times in the Peerage of England. It is particularly associated with two families: the Beauforts, who held the title from the creation of 1448, and the Seymours, from the creation of 1547, in whose name the title is still held. The present dukedom is unique, in that the first holder of the title created it for himself in his capacity of Lord Protector of the Kingdom of England, using a power granted in the will of his brother in law King Henry VIII.
The only subsidiary title of the current duke of Somerset is Baron Seymour of Trowbridge, which is used as a courtesy title by the eldest son and heir of the duke. This courtesy title is the lowest in rank of all heirs to dukedoms in the peerages of the British Isles, yet the holder's precedence is higher than his title suggests, by virtue of the seniority of the Dukedom of Somerset (the only more senior non-royal duke is the Duke of Norfolk).