While filming Silver Streak, Gene Wilder began writing a script during long waits in his trailer. The script was about “a baker from Milwaukee, in 1927, who wants to try out for a big Hollywood contest to find the next Rudolph Valentino. He takes his wife to Hollywood, tries out for the part, and his wife runs off with the real Rudolph Valentino. Years earlier, I had seen a film by Federico Fellini, starring Alberto Sordi, called The White Sheik, which had inspired this idea. I called my script The World’s Greatest Lover.”
Since The World’s Greatest Lover was inspired by Fellini’s The White Sheik, Wilder was concerned about any legal problems that may come up. After calling the legal department at 20th Century-Fox, he was told to get permission from Fellini just to be safe:
My dear friend Denise Breton said, “I know Federico—let’s call him up.” She picked up the phone in her office, and two minutes later I heard the voice of the great Fellini.
"I loved your Frankenstein. It was a great movie. You are a great actor.”
"Thank you. Signor Fellini, I need—"
"Thank you. Federico, I have a little problem. I was inspired by The White Sheik and wrote a film called The World’s Greatest Lover, and even though my story is almost completely different from yours, the legal department at 20th Century-Fox says I need some kind of permission from you—just in case.”
"Okay, Gene—here’s what you do: on the screen, in the opening titles, you write—in big letters—AND SPECIAL THANKS TO MY FRIEND FEDERICO FELLINI. That will take care of everything."
I did as he instructed. When the film opened and the audiences saw those lines…they laughed, thinking it was my little joke. But it wasn’t a joke. That’s what Federico wanted—that’s what he got. And I didn’t have any legal problems. (via Wilder’s 2005 memoir, Kiss Me Like a Stranger, 167-8)