Modern historians have called William Montague Edward's "most intimate personal friend"[3] and "the chief influence behind the throne from Mortimer's downfall in 1330 until his own death in 1344.

"[4] William Montagu, born at Cassington, Oxfordshire in 1301, was the second but eldest surviving son of William Montagu, 2nd Baron Montagu, and Elizabeth de Montfort, daughter of Sir Peter Montfort of Beaudesert, Warwickshire,[5] by Matilda/Maud de la Mare, daughter and heiress of Henry de la Mare of Ashtead, Surrey, Royal Justice, Seneschal of William Longspree II, Earl of Salisbury.

[9] The younger William was still a minor at the time of his father's death, and entered the royal household as a ward of the king in 1320.

The young king—along with his government—was under the dominance of his mother Isabella and her lover Roger Mortimer, who had been responsible for the deposition of the king's father.

After Montagu's return, Richard Bury, Keeper of the Privy Seal, wrote to inform the pope that only letters containing the words pater sancte (holy father), in Edward's own handwriting, were indeed from the king.

[13] Along with William de Bohun, Robert Ufford, and John Neville and others, he entered the castle, where he met up with the king.

[15] As a reward for his part in the coup, Montagu was given lands worth £1,000, including the Welsh lordship of Denbigh that had belonged to Mortimer.

[5] From 1333 onwards, Montagu was deeply engaged in the Scottish Wars, and distinguished himself at the Siege of Berwick and the Battle of Halidon Hill.

[21] To allow Montagu to support his new status, the king granted him land and rent of a value of 1,000 marks a year.

[22] A contemporary poem tells of a vow made by the earl on the eve of the wars – he would not open one of his eyes while fighting in France.

[23] In April 1337, Montagu was appointed to a diplomatic commission to Valenciennes, to establish alliances with Flanders and the German princes.

[24] In July 1338, he accompanied the king on another mission to the continent, again providing the greatest number of soldiers, with 123 men-at-arms and 50 archers.

[5] Reportedly, King Philip VI of France wanted to execute Salisbury and Robert Ufford, Earl of Suffolk, who was captured with him.

Philip was, however, dissuaded by John of Bohemia, who argued that the earls could come in handy in an exchange, should any French noblemen be captured.

[5] Salisbury had long been frustrated by the failure of the government in England to provide sufficient funds for the war effort.

[5] His final international commission took place late in 1343, when he accompanied Henry of Grosmont, Earl of Derby, on a diplomatic mission to Castile.

[18] The first Earl of Salisbury made enormous additions to the family fortune; at the time of his father's death, the lands had been valued at just over £300.

[33] Edward was also free with granting franchises to Salisbury, including the return of writs, which gave the earl authority in his lands normally held by the royally appointed sheriff.

[9] The children of William and Catherine were as follows:[36] Salisbury is a character in Les Rois maudits (The Accursed Kings), a series of French historical novels by Maurice Druon.