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Tilikum, an orca who became famous as a subject of the documentary "Blackfish," died this past week in Orlando. He was responsible for the death of a SeaWorld trainer and two other people, and his story and the public's reaction to it pushed SeaWorld to stop breeding killer whales in captivity. NPR's Greg Allen reports.

GREG ALLEN, BYLINE: Tilikum was about 36 years old, relatively old for a killer whale in captivity. SeaWorld said he'd been suffering from an apparent respiratory infection, but didn't give a cause of death. Tilikum became well-known to animal rights activists and the public through the documentary "Blackfish." That film examined the death in 2010 of SeaWorld trainer Dawn Brancheau. Following a show at the Orlando park Tilikum, a large male orca, pulled Brancheau into the water, where she died from blunt force and drowning. In "Blackfish," former SeaWorld trainer Jeffrey Ventre described working with Tilikum.

(SOUNDBITE OF DOCUMENTARY, "BLACKFISH")

JEFFREY VENTRE: He arrived, I think, in 1992. I was at Whale and Dolphin Stadium when he arrived. And he's twice as large as the next animal in the facility.

ALLEN: Brancheau was the third person killed by Tilikum. The first person killed was Keltie Byrne, a part-time trainer at Sealand of the Pacific, a Canadian park that's now closed. Byrne slipped into a pool containing Tilikum and two other orcas, where she was dragged around and drowned. The second person killed was at SeaWorld Orlando. A man named David Dukes (ph), who stayed in the park after it closed, was found the next morning on Tilikum's back, dead from drowning.

Naomi Rose is an orca biologist with the Animal Welfare Institute. She says it's clear from his behavior that Tilikum was frustrated and disturbed.

NAOMI ROSE: I don't know that he meant to kill the first two people. That really looked like some sort of play behavior, you know, and they drowned. But the third death, Dawn Brancheau, that was an attack. Who knows what was going on in his head? Again, pure speculation, but I do think that he's had a very grim life.

ALLEN: Animal welfare groups have long fought to stop SeaWorld and other marine parks from holding killer whales in captivity. 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. As a male, Tilikum was prized as a breeder, siring more than 20 calves. At SeaWorld Orlando, former trainer Jeffrey Ventre says the orca was kept isolated most of the time. Ventre, now a medical doctor, says Tilikum showed neurotic behaviors.

VENTRE: Chewing on concrete, breaking his teeth on the steel bars simply out of boredom. He got picked on a lot. And he was alone a lot. Humans in isolation or chimps in isolation begin to act abnormally. And that's what happened in his case, and it led to the death of three human beings.

ALLEN: Following Dawn Brancheau's death, the federal Occupational Safety and Health Administration issued rulings that prohibited trainers from working in the water with killer whales. 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. It's a major change in direction for SeaWorld.

Tim Zimmermann wrote about Dawn Brancheau's death for Outside Magazine and was one of the producers of "Blackfish." Despite the orca's troubled history, he always found a deep well of public sympathy for Tilikum.

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

ALLEN: In announcing his death, SeaWorld said Tilikum had a special place in the hearts of the staff at the theme park, but that his life will always be connected with the death of trainer Dawn Brancheau. Greg Allen, NPR News, Miami. Transcript provided by NPR, Copyright NPR.