Wow, Mr. Belding has really let himself go, huh? "Saved By the Bell's" principal, Dennis Haskins, shocked us with his appearance when he guest starred in Season 5 as a test-kitchen scientist in the Cool Whip laboratory. Guess those Bayside High school lunches weren't as healthy as we thought. Plus, he had to stand by awkwardly while Don and Peggy bickered, when we knew he just wanted to say, "Hey hey hey, what is going on here?"
The halls of Sterling Cooper & Partners have been filled with a lot of familiar faces lately. Here are more than 20 "Mad Men" guest stars we recognize from previous roles in TV and movies. — Dave Nemetz, Yahoo! TV