Robert de Ros (or of Roos) was the son of Everard of Roos and Roese Trussebut (d.1194). He was born circa 1182 and had a brother, Peter. The family had received inherited land at Helmsley (Yorks) and Wark (Northumberland) through marriage from Walter Espec. Robert succeeded to his lands in 1191. Robert was lord of Wark Castle and also bailiff and castellan of Bonneville-sur-Touques in Lower Normandy, through his mother. In 1200 he was married to Isabella, an illegitimate daughter of William I, king of Scots, and widow of Robert (III) Bruce. They had two sons: William, who had a son Robert; and Robert de Ros, baron of Wark.
See W. E. Rhodes, ‘Ros, Robert de (c.1182–1226/7)’, rev. Hugh M. Thomas, Oxford Dictionary of National Biography, Oxford University Press, 2004; online edn, Oct 2005 [http://www.oxforddnb.com/view/article/24077, accessed 26 Aug 2010]