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John Lithgow was the original choice to play Frasier on Cheers. He wasn't available due to his busy work schedule and the part went to Kelsey Grammer.
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Nancy Marchand, who played the Police Commissioner in The Naked Gun and more famously, Tony Soprano's mother on The Sopranos, guest starred as Frasier's mother. She disapproved of Diane.
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Kirstie Alley was the only main cast member of Cheers who never guest starred on Frasier. As a Scientologist, Ms. Alley disapproves of psychiatrists and therefore refused to appear on the show.
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