Stars like Will Ferrell, Matt Damon, Oprah Winfrey and Kermit the Frog all stopped by
Played: Milton Greene, starting in season 3's "Mamma Mia"
With Alec Baldwin playing against his own personal convictions as arch-conservative corporate overlord Jack Donaghy, it might have made sense to hire a Republican actor to return the favor as Milton Greene, the liberal arts college professor who was Jack's biological father. But Charlton Heston had died the year before, so "30 Rock" went the other way, getting the man who best known for being the epitome of '70s pop culture sensitivity as Hawkeye on "M*A*S*H," to play very much to type as Milton, whose Jimmy Carter biography "From Peanut to President" made Jack cringe even as he was happy to have a father figure in his life. Alda embraced the self-parodic nature of the role, most memorably in a scene in his second appearance when he referenced the dark plot of the "M*A*S*H" series finale by interrupting one of Tracy's rants to ask, "A guy crying about a chicken and a baby? I thought this was a comedy show."
- Alan Sepinwall