The titles of Earl of Hertford and Marquess of Hertford have been created several times in the peerages of England and Great Britain.
The third Earldom of Hertford was created in 1559 for Edward Seymour, who was simultaneously created Baron Beauchamp of Hache. His grandson William Seymour was subsequently created Marquess of Hertford and restored to the title of Duke of Somerset; the Marquessate became extinct in 1675 and the other three titles in 1750.
Edward Seymour, 1st Duke of Somerset, 1st Earl of Hertford, 1st Viscount Beauchamp KG, PC (1500 – 22 January 1552) was an English nobleman and politician who served as Lord Protector of England from 1547 to 1549 during the minority of his nephew King Edward VI. He was the eldest surviving brother of Queen Jane Seymour, the third wife of King Henry VIII and mother of King Edward VI.
Seymour grew rapidly in favour with Henry VIII following Jane's marriage to the king in 1536, and was subsequently made Earl of Hertford. On Henry's death in 1547, he was appointed protector by the Regency Council on the accession of the nine-year-old Edward VI. Rewarded with the title Duke of Somerset, Seymour became the effective ruler of England. Somerset continued Henry's military campaign against the Scots and achieved a sound victory at the Battle of Pinkie, but ultimately he was unable to maintain his position in Scotland. Domestically, Somerset pursued further reforms as an extension of the English Reformation, and in 1549 imposed the first Book of Common Prayer through the Act of Uniformity, offering a compromise between Protestant and Roman Catholic teachings. The unpopularity of Somerset's religious measures, along with agrarian grievances, resulted in unrest in England and provoked a series of uprisings (including the Prayer Book Rebellion and Kett's Rebellion). Costly wars and economic mismanagement brought the Crown to financial ruin, further undermining his government.