What is the origin of the format for television credits?

Question

When you watch tv dramas/comedies there are credits at the beginning. They show clips of the leading actors and run their names on the screen. Then, the last actors' name is shown in a different format. e.x. "...and Martin Sheen as President Bartlet."

Why do they use this particular format and where does it come from?

Answer 1

This site gives the history of screen credits and titles.

http://www.soc.org/opcam/04_s94/mg04_titles.html