So we all know Merlin of course but his last name still remains a mystery to me and to a lot of others. I did some research just to see if I could find anything useful and guess what?? I did. Merlin's last name is generally understood to be Ambrosius. This was the name used by Geoffrey of Monmouth, who combined the character of Myrddin Wyllt with a war leader named Ambrosius Aurelianus to create the Merlin character. In the TV show Merlin. Isn't that just crazy cool??