He's a Dunmer mercenary from the Skyrim DLC Dragonborn. He's talkative, snarky, mysterious, and of course sexy, on top of being the strongest mercenary. Oddly enough, he is one of two followers in the game who cannot be married. Not being able to marry the other one makes sense, but I don't know why Teldryn can't be married in vanilla. Of course, people made several mods concerning Teldryn, one including the option to marry him.