She is rarely mentioned on-air. She doesn’t have a funny nickname like producer Gary Dell’Abate’s “Baba Booey” nor is she endlessly teased and tormented like staff writer Benjy Bronk. Not even many longtime listeners know her name.

But to anyone close to Howard Stern, the self-proclaimed king of all media, Marci Turk is “The Howard Whisperer.” The chief operating officer of Mr. Stern’s Sirius XM Satellite radio operations, Ms. Turk has become something of a gatekeeper to the radio star and one of his most trusted advisers.

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