Since the moment she was born, Colo defied the odds. Through the mid-1950s, zookeepers did not believe it possible for a gorilla to be born and raised in captivity.

She wasn’t even supposed to have been conceived. But in 1956, Colo made history, becoming the world’s first gorilla born in a zoo. She bewildered animal experts and captivated the hearts of Americans for more than half a century, exceeding her life expectancy by two decades and living long enough to become a great-great grandmother.

On Tuesday, the Columbus Zoo and Aquarium announced that Colo, the oldest known living gorilla in the country, had died. She departed in her sleep overnight, less than a month after celebrating her 60th birthday.

Colo had a malignant tumor removed from under her arm on Dec. 3, but until a necropsy is performed, it is unknown if the cancer led to her death, the zoo announced in a news release. She will be cremated and her ashes buried in an undisclosed site at the zoo. The zoo has designated an area outside its entrance for anyone wishing to remember Colo, a name that is short for Columbus, Ohio.

Thousands of Columbus residents and Americans nationwide grieved the news of the death, recounting childhood memories of the beloved gorilla. On Facebook, the zoo’s announcement has been shared more than 25,500 times. In the more than 3,000 comments, mothers shared photos of Colo looking into the eyes of their children through the glass in her enclosure, holding up her hands to touch theirs. To those who met Colo, the gorilla displayed a tenacious personality, a sense of humor and a capacity to connect with visitors in remarkable ways.

One woman posted: “When my twin girls were just about 6 months old, (they are 21 yrs old now) took them to see the Gorillas. Colo brought a baby gorilla over to me and held it up to me. I held one of my twins up to her and she just stared at her. Then she cradled the baby gorilla and I cradled mine.”

Another woman spoke about her father, a former zoo director who was with her during heart surgery a day before he passed with congestive heart failure in 2009. She said she has worn Colo’s picture on her key ring ever since her father’s death. “We will always remember you Colo,” she wrote.

“Oh, sweet Colo, I remember visiting you after you were born,” one woman wrote. “I was 8. And now as a 68-year old I say ‘good-bye’ to you.”

Last month, hundreds of visitors — including Colo’s original nurse — gathered at the zoo to celebrate the gorilla’s 60th birthday. They watched and sang happy birthday as she opened presents and ate cake made with tomatoes (her favorite food) and apples in her enclosure, which was decorated with colorful streamers for the occasion. Multiple celebrities, including Betty White, who visited the zoo in 2014, recorded videos wishing the gorilla a happy birthday.

On Dec. 22, a star was born and we’re pulling out all the stops! A few other stars wanted to send their birthday wishes to Colo, too. To kick it off, here’s a message from Jungle Jack Hanna’s dear friend, Betty White! Join the birthday celebration on Thursday via live webcast here:

Posted by Columbus Zoo and Aquarium on Monday, December 19, 2016

“Colo touched the hearts of generations of people who came to see her and those that cared for her over her long lifetime,” the zoo’s president, Tom Stalf, said in a statement. “She was an ambassador for gorillas and inspired people to learn more about the critically endangered species and motivated them to protect gorillas in their native habitat.”

Before Colo’s conception, her parents, Mac and Millie, — both captured as infants in West Africa — were kept in separate cages at the zoo under the orders of the director, who feared the two gorillas might hurt each other. But a young zoo employee and second-year veterinary student, Warren Thomas, defied those orders, placing them together at night.

According to a New York Times story from the time, Colo’s birth on Dec. 22, 1956, came as a surprise. While Thomas was feeding the animals in the ape house, he noticed a 9-year-old female gorilla perched on an upper level of the enclosure. On the floor below lay her newborn daughter, a baby gorilla in her amniotic sack. Thomas rushed the baby to the zoo kitchen and tried to stimulate her into breathing by slapping her on the back. She caught her breath, but lost it again, so Thomas did the first thing that came to mind: He breathed into the lifeless gorilla’s mouth.

“I was all alone and knew that history was in the making, but I didn’t have time to think about anything but keeping the baby alive,” Thomas said, according to the article. “In about fifteen minutes, she was breathing.” Warren Thomas would later become the director of the Los Angeles Zoo.

Colo weighed four and a half pounds, and was quickly moved into an incubator. Zookeepers worried that Colo’s mother wasn’t up to the task of raising the baby in captivity, never having learned parenting skills from her own parents in the wild, so they built her a special nursery in the Columbus Zoo, according to Jeff Lyttle, who wrote a book about the Columbus Zoo’s gorillas, and spoke to PBS in 2008.

Her birth made international headlines; even Columbus Mayor M.E. Sensenbrenner passed out cigars with a message: It’s a girl. Zoo visitation skyrocketed — in 1957, more than 1 million people visited the world-famous gorilla, the Columbus Dispatch reported, and her caretakers dressed her up in an Easter bonnet and fancy dresses.

“Some people say she still likes to wear her food dish as a hat because she spent so much of her infancy wearing hats,” Lyttle said. Videos from the time period show her crawling around like a human infant, playing with toys and being bathed by her caretakers.

Colo’s birth forever changed how naturalists and zoo officials viewed gorilla births, and revealed to animal scientists for the first time the length of a gorilla’s gestation period. It would be more than five years before the next gorilla would be born in a zoo, and another five years before a third gorilla was born in a zoo. Today, more and more, captive gorilla babies are being raised by their own mothers, as zookeepers improve their ability to recreate natural conditions.

There are approximately 350 gorillas of all species in accredited zoos across the United States and an estimated 150,000 to 250,000 Western lowland gorillas left in the world, the zoo said in a statement. Gorillas are listed as endangered due to loss of habitat, poaching, and susceptibility to diseases.

During the course of her exceptionally long lifetime, Colo became a mother of three, grandmother of 16, great-grandmother of 12, and great-great-grandmother of three. Since she had been at the zoo longer than any other creature, Colo was often referred to as “The Queen.” And fittingly, she always got her wish: to be left alone. But that didn’t mean she didn’t enjoy the company of those who visited her and cared for her. As Matt Tullis wrote in the Columbus Dispatch for the gorilla’s 50th birthday, each zookeeper developed a close relationship with Colo.

Recalling favorite stories about Colo, one caretaker spoke of the time Colo took a toothbrush out of her hand and began brushing her own teeth. Another, Mike Zedekar, tells the story of how a few years before, Colo wore a ball cap. Zedekar would always wear a cap at work and, one day, while he was cleaning outside her cage, he turned it backward. Colo did the same. He turned it sideways, and she copied him once more. Once she no longer had a hat of her own, she would try to take his whenever he walked by.

Dan Nellis told the Columbus Dispatch that when he started at the zoo, in 1992, he was the first male keeper to work with Colo since 1979. She spit on him for two years, he said.

“Then she figured out I wasn’t going to leave and she started hitting on me,” he said. “They tell you not to get attached, but you can’t help it.”

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