Boris, a beloved elderly polar bear who lived at Tacoma’s Point Defiance Zoo & Aquarium for 18 years, was euthanized Tuesday after a “significant decline in his health,” zoo officials said.

Recent exams showed Boris, who was 34 years old, suffered significant arthritis in his joints and had several fused vertebrae in his neck and skin, according to a Tuesday statement from the zoo. He also had a history of gastrointestinal problems and dental and liver disease. 

“We cared for Boris as long as possible with a combination of groundbreaking medical treatment and daily TLC,” Dr. Karen Wolf, the zoo’s head veterinarian, said in the statement. “But he had increasing difficulty getting up, had recently fallen, and his quality of life had declined dramatically. We did not want him to suffer. His loss will be felt deeply around the zoo.”

Experts believe Boris was the oldest male polar bear in human care on the planet, the statement said. According to the zoo, male polar bears usually live about 23 years in human care — and about 15 to 18 years in the wild.

“This is a very sad day for us,” said Alan Varsik, director of zoological and environmental education for Metro Parks Tacoma, in the statement. “Boris held a special place in the hearts of our staff and our community.

Point Defiance Zoo welcomed Boris in 2002 after the U.S. Fish & Wildlife Service seized him from a traveling circus that had stopped in Puerto Rico. At the time, he was scrawny and malnourished, the zoo said. 

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“Zoos across the nation stepped up to take Boris and five other bears, providing homes, proper nutrition and expert care,” the statement said. “Boris was the last surviving member of that group.”

Boris made headlines again in 2013 when he underwent a 4 1/2-hour root-canal procedure. In late 2017, Wolf — with the help of a Colorado State University researcher — used stem cells grown from Boris’ own fat tissue to try and treat his arthritis.

While stem-cell therapy has been used to care for other animals, researchers believe Boris was one of the first polar bears to receive the treatment, the statement said.

During Boris’ time at the Tacoma zoo, he enjoyed rolling in wood shavings, splashing around in his saltwater pool and playing with barrels, cans and balls, the zoo said. He also enjoyed an “occasional mouth-wrestle” with Blizzard, another polar bear at the zoo. 

Blizzard, now 24 years old, still lives in the zoo’s Arctic Tundra habitat.

The zoo’s veterinary team is planning to perform a necropsy on Boris to “help with future polar bear conservation,” the statement said. 

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“We took Boris from a bad scenario to a place where he had a better life, and where he could be an ambassador for the Arctic,” Mike Messersmith, a staff biologist and one of Boris’ caretakers, said in the statement. “He inspired people to help save his species by taking actions to slow climate change.”

Polar bears, which are protected by the U.S. Marine Mammal Protection Act, are listed as a threatened species under the U.S. Endangered Species Act — an addition made in 2008 because of melting sea ice.

Zoo guests can sign a card for Boris’ caregivers in memory of the bear in the zoo’s main plaza from Wednesday to Friday, and donations can be made toward polar bear conservation at thezoosociety.org/donate