Phyllis
Originally, Phyllis Smith started out as a casting associate on the show. The producers ended up being so impressed with her that they created the role of Phyllis Vance especially for her on the show. Before that, she was a burlesque dancer and NFL cheerleader.
Wig
For half of season three, John Krasinski had to wear a wig due to the fact that he shaved his head for a role he was shooting at the time.