Board Thread:Questions and Answers/@comment-9431245-20130628182556/@comment-124.149.85.241-20140228062402

He was never given one in the show, probably because he was a peasant (and a fatherless one at that) but he 's always been known as Merlin Emrys (also Ambrosius) but they sort of split the names so Emrys was what the druids knew him as.

I think Arthur was the only one with a surname, I can't remember if Morgana had one.