Robert Cox

(male) One of the many French names of Germanic origin that were introduced into Britain by the Normans; it has since remained in continuous use. It is derived from the nearly synonymous elements hrōd ‘fame’ + berht ‘bright, famous’, and had a native Old English predecessor of similar form (Hreodbeorht), which was supplanted by the Norman name. Two dukes of Normandy in the 11th century bore the name: the father of William the Conqueror (sometimes identified with the legendary Robert the Devil), and his eldest son. It was borne also by three kings of Scotland, notably Robert the Bruce (1274–1329), who freed Scotland from English domination. The altered short form Bob is very common, but Hob and Dob, which were common in the Middle Ages and gave rise to surnames, are extinct. See also Rupert.

English: from Cocke in any the senses described + the suffix -s denoting ‘son of’ or ‘servant of’.