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.

As Mr. Stern tries to broaden his appeal and soften his image, some fans are complaining Ms. Turk has cleaned up the shock jock and made him safe for the kind of celebrities he used to mock. With Mr. Stern devoting more of his show to being a serious interviewer, Ms. Turk is often accused in chat rooms of making him more politically correct. In February, for example, Mr. Stern spent 90 minutes interviewing “Girls” star and creator Lena Dunham who later called him a “feminist.” Musician Sheryl Crow and actor Steve Martin have been guests. Lengthy celebrity interviews mean less time for his usual high jinks.

Mr. Stern mentioned Ms. Turk on air two weeks ago in a diatribe at listeners who miss the old Howard. “The new thing from the people who now hate me is, ‘oh Howard changed because of Marci Turk … he got this woman in there and she calls the shots on the show and she won’t let him do this or that,’ ” Mr. Stern said on his April 19 show. The show’s subjects, he continued are “where I want to go.”

“It seems like all the drama around her has to do with the longstanding Howard Stern aficionados,” says Eric Sherman, a longtime talent manager whose clients have included Aerosmith lead singer Steven Tyler, who has often appeared on the show. “Under her watch, he has excelled,” he adds.