He appears as witness to a charter of Jocelin, Bishop of Glasgow in 1174 in favour of the monks of Kelso Abbey, at which time he was in possession of the Lands of Douglas.
[1] It seems he was the son of Theobald le Fleming (born 1120, Aldingham Manor, Lancashire, England died 1193, Douglasdale, Midlothian, Scotland) and his wife, the sister of Freskin de Kersdale (of Moray).
The earlier historians may have confused the mythic Donald Bain with Domnall Bán mac Domnaill, the penultimate Meic Uilleim chief.
This may be corroborated by the facts that the lands of Douglas marched with those of the leader of King William I of Scotland's retaliatory forces, Lochlann, Lord of Galloway.
Although William de Douglas was the first known owner of Douglasdale, holding that land between 1174 and 1213, there is no reason to doubt that his father was "Theobaldo Flamatico" or Theobald the Fleming.