On Monday morning, celebrities took to social media to mourn the loss of the Classic Hollywood icon Doris Day, who died of complications from pneumonia at 97 years old.

Day's public image went hand in hand with purity and innocence—and the wholesome midcentury blockbusters she starred in bolstered that, making her a sort of chaste foil to Marilyn Monroe's pinup persona—but her real disposition could not have been further from her constructed persona for the cameras. (She once quipped in her 1976 memoir, “I have the unfortunate reputation of being Miss Goody Two-Shoes, America’s Virgin, and all that, so I’m afraid it’s going to shock some people for me to say this, but I staunchly believe no two people should get married until they have lived together.")

The actress is best known for her illustrious film career—including starring roles in Calamity Jane in 1953, Alfred Hitchcock's 1956 thriller The Man Who Knew Too Much, and Pillow Talk with Rock Hudson in 1959—and for her jazz discography, which includes her popular recording of "Que Sera, Sera (Whatever Will Be, Will Be)," but what may be less known is her history as a lifelong animal welfare activist.

On social media, celebrities from Goldie Hawn to Sarah Jessica Parker remembered Day not only for her talent but also for her unfettered commitment to loving animals, too.

Celebrities seem to be showing extra appreciation for the fact that Day once wore a shirt that read "Be kind to animals or I'll kill you." (This same slogan has also appeared on a T-shirt that the outspoken meat-free musician Morrissey attempted to sell as merch in his online store, only to eventually be accused of copying Day, since she wore it first.)

Day's love of animals extends back to her childhood (“I've never met an animal I didn't like, and I can't say the same thing about people," is one popular quote often attributed to the actress). Once she became an established Hollywood figure, she used her star power to advocate for animals on set. According to Day, she once told Hitchcock that she couldn't continue working on The Man Who Knew Too Much if the horses, donkeys, and dogs used for the film were not treated with respect and properly fed.

Doris Day with her horse, Silver, during filming of David Butler's musical Calamity Jane, 1953.

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From 1968 to 1973, Day led her own sitcom, The Doris Day Show, which chronicled the life of a city dweller who moves to a California ranch. The series presented plenty of opportunities for her to work with animals on set—from dogs to horses to monkeys—and ultimately inspired her to found nonprofit organizations that would advocate for better treatment for working animals in Hollywood. Before it was something of a trend to even publicly condemn the wearing of fur, Day cofounded an animal welfare nonprofit organization called Actors and Others for Animals, in 1971, and founded the Doris Day Pet Foundation (which has since been renamed the Doris Day Animal Foundation) seven years later.

Doris Day cradles a monkey as Doris Martin, her character on The Doris Day Show, in an episode titled "Doris Leaves Today's World," August 5, 1970.

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With her foundation, Day started World Spay Day (an entire day dedicated to reminding pet owners to neuter their cats and dogs, lest they place more animals at higher risk of being euthanized in shelters), worked to shut down puppy mills, supported a bill that would ban the slaughter of wild horses, and advocated for more pet-friendly hotels (one of which is Cypress Inn, which she co-owned in Carmel, California, for over 20 years). She often fostered pets in her own home, and became known as "the Dog Catcher of Beverly Hills," according to her foundation. Her foundation also joined forces with the Humane Society and, in 2005, when Hurricane Katrina devastated Louisiana, the DDFA provided aid to dogs and cats by airlifting the pets to safe ground, according to an interview that Day gave to a dog culture magazine in 2006.

Doris Day with one of her dogs at a press conference at the dog-friendly hotel she owned in Carmel, California, July 16, 1985.

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According to the DDFA, which confirmed her death via email on Monday morning, Day requested “no funeral or memorial service and no grave marker.”

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