Board Thread:Questions and Answers/@comment-9431245-20130628182556/@comment-5102537-20131019113430

I doubt that he had a surname. I know that it's a re-telling and not everything on the show was accurate to the real dark ages, but Gwen, Gaius, Gwaine, Percival, Balinor and so many others weren't provided with a surname either. I think that they stuck to the fact that in those times, surnames were uncommon until the Normans brought them the tradition of using surnames.

The reason why the nobles on the show had surnames may be because they wanted to be addressed by either their title or to distinguish themselves from the commoners. Moreover, in some legends, Uther was the son of a Roman emperior and probably decided to keep at least two names (although Uther Pendragon wasn't his real name according to the legends). Some other nobles had their names extended by "of (somewhere)". Lancelot and Gorlois' names were of French origin and I don't know when those regions had started to use surnames. We don't even know the surname of Caerleon, Cenred, Olaf and others. Maybe the use of at least two names was a sign of progress and culture and contributed to the fact that Camelot, on the show, was the most progressed and civilised kingdom.

Here is what history says:

"Formation of Surnames 

The Anglo-Saxons used only personal names, sometimes with nicknames and patronymics, so it was not until after the Norman Conquest that inherited surnames were adopted. Originally these were only borne by nobles and were likely to be restricted to the place of origin, preceded by ‘de’ as in modern French, or the father’s name preceded by ‘Fitz’ (from French fils 'son').

Later, sources included:

The link can be found here but you have scroll down:

http://www.infernaldreams.com/names/Europe/Medieval/England.htm