William, 8th Earl of Douglas

William succeeded his father with the aim of restoring to the family the possessions forfeited after the Death of William, 6th Earl of Douglas. He regained the Lordship of Galloway by marrying the sister, Margaret, and heiress of the victims of the Black Bull's Dinner. His holdings were further enhanced by his brothers who became, in turn, Bishop of Aberdeen, Earl of Moray, Earl of Ormond and Lord of Balveny. 

In 1447 war once again broke out between Scotland and England. The 8th Earl proved to be the hero in the Scot's burning of Alnwick and Warkworth in retaliation for English aggression. His brother, Earl of Ormond, defeated an English invasion at the Battle of Sark. 

In 1450 the 8th Earl led a Scottish retinue to Rome in celebration of the end of the Papal schism. King James II, growing wary of the Douglas power, took the opportunity to assert his authority by seizing and destroying a number of Douglas strongholds. On his return to Scotland, William, now distrustful of the King, made a pact against him with Alexander Lindsay, Earl of Crawford and John, Lord of the Isles. He also made contact with the Yorkists in England. James II learned of the Earl's maneuvering and summoned him to Stirling Castle with a promise of safe conduct. 

On February 22, 1452 the Earl dined with the King and then retired with him to a small antechamber. There the King revealed his knowledge of Douglas' dealings and asked him to reaffirm his loyalty by renouncing his band with Crawford and the Lord of the Isles. When Douglas refused the King became enraged and stabbed the Earl in the throat. The King's Captain of the Guard, hearing the scuffle, burst into the room and finished Douglas off. He then threw Douglas' body from the window into the garden below.

A poem imagines the Earl's refusal...

'No, by the cross it may not be;
I've pledged my knightly word',
And like a thundercloud he scowled,
And half unsheathed his sword.
Then drew the King that jewelled glaive,
Which gore so oft had spilt
And in the haughty Douglas' heart
He sheathed it to the hilt.

2nd version

The power of the Black Douglases was restored by the 8th earl, who recovered Wigtown, Galloway and Boti1well by marriage (by papal dispensation) with his cousin, the Fair Maid of Galloway. He was soon high in favour with James II., and procured the disgrace of Crichton, his kinsmen’s murderer, by an alliance with his rival, Sir Alexander Livingstone. In 14~o James raided the earl’s lands during his absence on a pilgrimage to Rome; but their relations seemed outwardly friendly until in 1452 the king invited Douglas to Stirling Castle under a safe-conduct, in itself, however, a proof of strained relations. There James demanded the dissolution of a league into which Douglas had entered with Alexander Lindsay, the ~‘ Tiger” earl (4th) of Crawford. On Douglas’s refusal the king murdered him (February 22) with his own hands, the courtiers helping to despatch him. The tales of the hanging of Sir Herbert Herries of Terregles and the murder of McLellan of Bombie by Douglas rest on no sure evidence.

Source: http://21.1911encyclopedia.org/D/DO/DOUGLAS_SIR_CHARLES.htm