General Notes

Sir William Douglas, Lord of Nithsdale, died c1392, illegitimate son of Sir Archibald Douglas, "The Grim," 3rd Earl of Douglas, who was the illegitimate son of Sir James Douglas, Lord of Galloway.  Known to the Scots as "good Sir James" and to the English as "The Black Douglas," he was, with Wallace and Bruce, one of the three great heroes of Scottish Independence.  [Magna Charta Sureties]

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Copied from "Douglas Family" by Mark Freeman, freepages.genalogy.rootsweb.com/~markfreeman/douglas.html:
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Lord of Nithsdale ; "Natural son of Sir Archibald Douglas" ; King Robert, along with the hand of his daughter, bestowed upon Douglas the lordship of Nithsdale, and also appointed him Warden of the West Border, and Sheriff of Dumfries.

"After a truce was made with England, he joined the Teutonic knights in their crusade against the Pagans in Prussia and Lithuania, and was appointed admiral of their fleet. He is said to have been created Duke of Prussia and Prince of Dantzic for his services in raising the siege of that town and expelling the Pagans from the district. His countrymen were also thenceforth made freemen of Dantzic. He was murdered at Dantzic, about the year 1392, by a band of assassins hired by an Englishman, whom Fordun terms Lord Clifford, who had fastened a quarrel on him."
The Great Historic Families of Scotland, James Taylor