Tilikum, possibly the most famous orca in the world, has died, according to SeaWorld Orlando.

He was the subject of the influential documentary Blackfish, and outcry over his story prompted SeaWorld to stop breeding orcas in captivity.

Tilikum was estimated to be 36 years old, SeaWorld said in a statement, which is old for a captive killer whale. He faced "very serious health issues," the park says, and had been declining for months.

The orca died Friday morning surrounded by trainers and veterinary staff. A necropsy is required to determine the official cause of death, but he had suffered a "persistent and complicated bacterial lung infection," the park says, which had been treated by a range of medicines and therapies.

Tilikum was 22 feet long and weighed more than 11,000 pounds, according to The Associated Press. He was born off the waters of Iceland, captured and performed in captivity for decades — first at the now-defunct Sealand of the Pacific and then at SeaWorld Orlando. A prolific breeder, he sired more than 20 calves.

But he became notorious for aggressive behavior. In the '90s, he was implicated in two deaths: a trainer who drowned and a man who was found dead in his tank.

Then, in 2010, he killed SeaWorld trainer Dawn Brancheau, holding her underwater until she died of drowning and blunt force trauma.

In the immediate aftermath of that incident, the question was whether Tilikum would be put down, and whether he would return to performing, as he did in 2011.

But then a 2013 documentary called Blackfish changed the narrative around aggressive behavior by orcas, and by Tilikum in particular.

In the film, former trainers at SeaWorld criticized the park's practices as harmful for orcas and dangerous for trainers. They argued that animals such as Tilikum behaved aggressively because of the stress and trauma of captivity.

As NPR's Greg Allen reports, animal welfare groups have long protested against marine parks holding killer whales in captivity at all. When Blackfish came out — and aired on CNN, where it reached millions of viewers — the public joined in the outcry.

The park has denied allegations that it mistreated orcas, but it did shift its position on captive breeding.

Greg reports:

"Orcas are an intelligent, social species that spend much of their life in family groups and in the wild range over thousands of miles. Advocates say holding these huge mammals in a tank is cruel. ...

"Activists stepped up their campaign against SeaWorld following the release of Blackfish. Attendance dropped at the park, a decline the company attributed in part to public reaction to the film. In response, SeaWorld's new CEO Joel Manby announced the company was ending its orca breeding program — making this the last generation of killer whales at its parks.

... Following SeaWorld's decision to end its orca breeding program, [Jeffrey] Ventre and three other former SeaWorld trainers issued a statement. 'We'd like to send love to Tilikum,' they wrote. 'In the end, his message was heard.' "

Members of the public and former SeaWorld trainers also called for Tilikum to be released back into the wild, but SeaWorld says its captive orcas could not survive in the open sea.

Tim Zimmerman, who wrote about Brancheau's death in Outside magazine and was a producer on Blackfish, told Greg there was a deep well of public sympathy for Tilikum.

"I think that's the most amazing thing that comes out of Tilikum's story," he said. "He killed three human beings. And yet when you learn about his life story, he does become the victim and you do sympathize with him."

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