William was the elder son of Nicholas II de Soules, Lord of Liddesdale and Butler of Scotland, and a cousin of Alexander Comyn, Earl of Buchan.
He remained in English service in the following decade, and received reward in 1312 with a knighthood and the lands of Sir Robert Keith although by that time those were in the hands of the Scots.
Scottish Borders folklore maintains that a Soulis was involved with the black arts being schooled with Michael Scot, the "wizard of the North".
In retaliation for a long history of cruelty, locals boiled this Lord Soules alive at Ninestane Rig.
[3] The more likely culprit would have been Sir Ranulf (Randolph) de Soules of Liddel (born c.1150 and murdered by his servants in 1207/8)[citation needed] Soulis is also said to have defeated the Northumbrian giant, The Cout o' Keilder.