17-year-old lion, Luke, dies at the National Zoo this week.

/ Smithsonian National Zoo

A male lion at the National Zoo was euthanized Wednesday after years of grappling with spinal disease, the zoo said in a Friday press release. At 17 years old, Luke the lion had been under the zoo’s care since 2006.

“Luke was truly the ‘king’ of the Great Cats exhibit,” said zoo curator Craig Saffoe in Friday’s release. “He was gentle with his mates, Naba and Shera, and an extremely patient and protective father to all 13 of the cubs he sired.”

Luke had been sick for years before his death this week.

In 2016, a CT scan revealed a lesion on the lion’s spine — an indication that a disc was damaged. At the time, surgery was deemed too risky. But this week, after noticing Luke had lost a significant amount of weight, staff found “several cystic masses throughout his liver” and “moderate-to-severe progression of his spinal condition.” Staff determined Luke’s overall quality of life long-term would be poor, and decided to euthanize him humanely.

When Luke first arrived to the National Zoo more than a decade ago, he was “the most genetically valuable lion in the North American population” because his genes hadn’t been introduced to U.S. zoos.

He sired 13 cubs that were transported to other North American zoos for breeding and research.

His death comes after the loss of Naba, an 18-year-old female lion, and the passing of infamous escape artist Rusty, the red panda.

Worldwide, lion populations have declined by 30%, with an estimated 20,000 remaining in the wild.

“Luke has left a lasting legacy,” Saffoe said. “Not only in the cubs he contributed to his species’ survival but also in the millions of visitors who were able to gain a deeper knowledge of and appreciation for African lions because of who he was as the patriarch of his pride.”

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