Henry Percy, 1st Earl of Northumberland, 4th Baron Percy, titular King of Mann, KG, Lord Marshal (10 November 1341 – 20 February 1408) was the son of Henry de Percy, 3rd Baron Percy and a descendent of Henry III of England. His mother was Mary of Lancaster, daughter of Henry, 3rd Earl of Lancaster, son of Edmund, Earl of Leicester and Lancaster, who was the son of Henry III. Henry Percy married Margaret Neville, daughter of Ralph Neville, 2nd Baron Neville de Raby and Alice de Audley. They were the parents of Henry Percy, nicknamed "Harry Hotspur".^[2]

Henry Percy was originally a follower of Edward III of England, for whom he held high offices in the administration of northern England. At a young age he was made warden of the marches towards Sctland in 1362, with the authority to negotiate with the Scottish government. In February 1367 he was entrusted with the supervision of all castles and fortified places in the Scottish marches. He went on to support King Richard II and was created an Earl and briefly given the title of Marshal of England. After Richard elevated his rival Ralph Neville to the position of Earl of Westmorland in 1397, Percy supported the rebellion of Henry Bolingbroke, who became King as Henry IV.

On King Henry IV's coronation he was appointed Constable of England and granted the lordship of the Isle of Man. Percy and his son, Henry Percy, known as "Hotspur", were given the task of subduing the rebellion of Owain Glyndŵr, but their attempts to make peace with the Welsh rebels did not meet with the king's approval. In 1403 the Percys turned against Henry IV in favour of Edmund Mortimer, 5th Earl of March, and then conspired with Owain Glyndŵr against King Henry.

The Percy rebellion failed at the Battle of Shrewsbury, where Hotspur was killed. Since the earl did not directly participate in the rebellion, he was not convicted of treason. However, he lost his office as Constable. In 1405 Percy supported Richard le Scrope, Archbishop of York, in another rebellion, after which Percy fled to Scotland, and his estates were confiscated by the King.

In 1408 Percy invaded England in rebellion once more and was killed at the Battle of Bramham Moor. Percy's severed head was subsequently put on display at London Bridge.

Northumberland is a major character in Shakespeare's Richard II, Henry IV, part 1, and Henry IV, part 2.

His position as a character in the Shakespearean canon inspired the character of Lord Percy Percy, Duke of Northumberland in the historical sitcom The Black Adder, set during the very late Plantagenet era.

The novel Lion of Alnwick by Carol Wensby-Scott is the first volume of the Percy Saga trilogy which retells the story of "the wild and brilliant Percy family" and relates a fictionalised account of the 1st Earl of Northumberland and his son Henry "Hotspur" Percy's lives. The other novels in the trilogy, Lion Dormant and Lion Invincible tell the story of his other descendants and their role in the English War of the Roses.

Henry Percy and his son Hotspur are also essential characters in Edith Pargeter's novel, A Bloody Field by Shrewsbury which recounts the events leading up to the Battle of Shrewsbury in 1403.

Alnwick Castle, the traditional home of the Percy family, was featured in the Harry Potter movies as the location of Hogwarts.

• Towson, Kris Henry Percy, first earl of Northumberland : ambition, conflict and cooperation in late mediaeval England St Andrews PhD Thesis, 2005.

• Rose, Alexander Kings in the North – The House of Percy in British History. Phoenix/Orion Books Ltd, 2002, ISBN 1-84212-485-4 (722 pages paperback)

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