Cook was known for many roles, among them the grandmother in "16 Candles," a potential client of Richard Gere in "American Gigolo" and a dairy farmer in Disney's animated film "Home on the Range."
Over the years, she also helped raise money and awareness for those battling HIV and AIDS.
Cook died of heart failure just three days shy of her 99th birthday.
She was born Mildred Frances Cook but her good friend Lucille Ball suggested she borrow a new stage name from Carole Lombard.
Cook was also a favorite of the theater - and the second woman to star in a production of "Hello, Dolly" after Carole Channing.
The role came with age and she relished it.
"You don't have to fight for it. You've lived it," she told ABC7's George Pennacchio. "And, honey, I could still wear that red dress and fly around that stage."
She was a frequent guest on Lucy's shows and many others, including "Dynasty," "Cagney & Lacey," "Charlie's Angels," and "Grey's Anatomy."
She continued acting into her 90s, appearing on an episode of "Major Crimes" in 2014.
Cook is survived by her husband, actor and writer Tom Troupe, whom she married in 1964.