There is much argument and discussion concerning the origin of the name and of the first of Douglas. The most popular, and the most romantic, comes to us from Scottish lore, some three hundred years before the first recorded Douglas records. This story of the origin is drawn, mainly from the work of David Hume, known as "Hume of Godscroft". Hume died in 1630 A.D. and was the private secretary, and confidant, to three successive Earls of Angus and was directly related to the Douglas Family. He had direct access to all of the family charters, legends, memorials and all other documentation available at Douglas Castle. As history was passed from generation to generation by story and song, it appears that Hume had first hand knowledge of this. Unfortunately Douglas Castle burned in 1775 with the loss of most of this information. Hume's original manuscript survived.

Hume sets the year as 767 A.D. with Sholto making his way across country with his sons and some of his followers. Sholto, by chance, came upon a battle in progress between King Solvanthius, of what was then Scotland, and the usurper, one Donald Bane (Donald of the Fair Hair), self proclaimed King of the all of the western islands (Ebudes and Hebrides). As Sholto watched the battle unfold, it became obvious that King Solvanthius was losing and Donald Bane was on the verge of a resounding victory. Sholto, and his followers, entered the battle and fought their way to Donald Bane whom Sholto killed. Bane's army was defeated , routed and dispersed. Afterwards King Solvanthius inquired of one of his lieutenants as to who had saved the day. His lieutenant pointed to Sholto and said "Sholto An Duine Du Glasse" (Behold The Dark Gray Man) referring to the clothing he was wearing and his appearence. From that day forward he was known as "Shotlo Duglass" and was granted many lands and titles. This Sholto is said to have had two sons, Hugh and William. Hugh went on to found the Douglas Clan in Scotland and William founded the Douglasi Scoti in Italy. Hume insist that the House of Douglas sprang from this man.

There has been a second explanation ,put forward, that in Gaelic, Du Glasse means black water and that the name refers to the color of the various rivers and streams in Lanarkshire. It is still a fact that Hume is one of few people to have had access to all of the Douglas Family history and genealogy.