CHARACTER NAMES are just that-- tags to identify who's speaking. They're always in caps, they should begin around four inches from the left edge of the page. You don't use a character's full name in a dialogue slug line. What you call a character depends on how you want the reader to feel about him or her-- "Stefan" and "Gartner" and "Mr. Gartner" inspire three different levels of closeness to the character. The character name is always in CAPS, it should begin around four inches from the left edge of the page, and nothing else goes on that line, except occasionally an Extension.