Earl of Salisbury is a title that has been created several times in British history. It has a complex history, being first created for Patrick de Salisbury in the middle twelfth century. It was eventually inherited by Alice, wife of Thomas, Earl of Lancaster. When the Earl of Lancaster lost his titles and was executed for treason in 1322, the Countess surrendered all of her titles to the King, and the titles lapsed.
The title was created for a second time in 1337 for William Montacute. It was inherited later by Richard Neville the Kingmaker, upon whose death the title went into abeyance because multiple individuals were entitled to inherit it.
Then, in 1472, it was granted to George, Duke of Clarence, who was married to Warwick's eldest daughter. When the Duke of Clarence was executed in 1478 for treason (supposedly by being drowned in a vat of Malmsey wine), the title was forfeit. It was then granted to Edward of Middleham (who was his nephew via the Duke's brother Richard), who died in 1484 at the age of 11.
It was restored to two of George of Clarence's children: to his son Edward in 1485 until his execution for treason in 1499, and to Edward's sister, Margaret Pole, Countess of Salisbury, in 1513 until she was also executed, and the title again forfeited, in 1539.
In 1605 the title was given to Robert Cecil, 1st Earl of Salisbury, a close advisor to James I. Cecil was a son of Queen Elizabeth I's chief advisor, William Cecil, 1st Baron Burghley. For information on this creation, see the Marquess of Salisbury.