In Southwest Montana, beneath the snow-capped peaks of the Rocky Mountains, is a 113,000-acre plot of rugged grassland called the Flying D Ranch. Its rolling meadows are grazed by bison, its thick woodland shelters a pack of wolves, and its crystalline streams teem with trout.
It's a landscape that probably looks much as it did two centuries ago, a vision that wouldn't be out of place in an oil painting of the old American West. But it wasn't always this way. Not so long ago the ranch was lined with wire fences and filled with cattle. That was before it was bought by Ted Turner.
If you don't know much about the man, it's hard to imagine a less likely environmentalist.
Read: Ted Turner - 'a huge victory for the land we love'
For much of his life, Turner was known to the world as a brash billionaire nicknamed the "Mouth of the South."
He was the media mogul who revolutionized cable TV and founded CNN, the world's first 24-hour news network. He was a hard drinker and a womanizer with three marriages under his belt. He was an action man -- a hunter, an America's Cup-winning sailor and the owner of a baseball, basketball and ice hockey team.
Yet Turner says that all the while, he had a master plan: to make the world a better place.
Watch: Why Ted Turner wants to save everything
A philanthropist of extraordinary generosity, he once donated $1 billion to the United Nations when the United States was in arrears of its payments. He founded the Nuclear Threat Initiative to reduce the risk from weapons of mass destruction, set up the UN Foundation to support humanitarian work around the world, and has signed The Giving Pledge, committing more than half his wealth to good deeds.
But the cause closest to his heart is protecting the earth, and the creatures we share it with.
"It's a pretty wonderful world that we live in down here, and it's worth saving," he tells CNN's Dr. Sanjay Gupta, reflecting on his decades of conservation work.
In pictures: Protecting native wildlife
Aged 80, his motto is "save everything" -- an adage he literally has as a bumper sticker. It may sound idealistic but the reasoning behind it is pragmatic: "You have to save the species that live on the planet to save the planet," he explains.
But while Turner's lofty goal is to conserve all species, there is one in particular whose survival is of special importance to him: the American bison.
"When I was a little boy, about 10 years old, I read National Geographic magazine and it had an article about bison, and it said how close they came to extinction," Turner recalls.
"I decided then that I would do what I could to help bring the bison back and preserve them."
Scientists believe that more than 30 million bison once roamed the great plains of North America. Migrating in vast herds, for millennia the largest creatures on the continent shaped the rugged landscape around them and provided sustenance for the Native Americans who hunted them.
But in the course of just a few decades, European settlers slaughtered almost all of them. At the start of the 20th century, only 1,000 bison remained.
Turner realized early on that preserving the bison meant finding a safe haven for them: he would need land -- and plenty of it.
"I had to make a lot of money first because ranches are not cheap," he says.
Starting in the mid-1980s, when he was an established media man, Turner began buying great swathes of ranch land in Montana, to restore it to the wild grassland it once was.
He encouraged the return of native plants and re-introduced indigenous animals -- chief among them his beloved bison.
Actor and activist Jane Fonda was Turner's third wife from 1991 to 2001, and spent much of her time with him on his ever-expanding ranches. "He wanted the land so that he could take down the fences, remove all of the signs of mankind, and to the extent possible return them to how they were before white Europeans came long and started developing them," she says.
"I would sometimes sit on the porch of his flagship ranch, the Flying D in Montana, looking over this amazing valley and the Spanish Peaks and envisioned what would've happened to this land if he hadn't bought it. There would've been 800 ranchettes and roads, and where would the critters have gone? Where could the herds of bison have gone?"
Turner now owns 16 ranches in six western states (and three more in Argentina). They cover a total of almost 2 million acres -- 10 times the size of New York City -- making him the second-biggest landowner in North America.
Each ranch is a refuge for native species, from the iconic -- like his beloved bison and gray wolves -- to the underappreciated -- like the black-footed ferret, the westslope cutthroat trout, and the bane of many a rancher, the prairie dog. For Turner, they are all welcome.
"Prairie dogs are considered pests by a lot of people because they eat grass and they eat a lot of it," he says. "But I feel like the prairie dogs are entitled to some. I'm willing to share my grass with the prairie dogs and the bison."
Fonda explains that Turner has a keen understanding of the way species interact with each other to sustain their habitat.
"Ted taught me so much," she says. "One of the important things that he taught me was the existence of what's known as keystone species -- certain species, that if they disappear the ecosystem collapses. He taught me that prairie dogs are a keystone species and they were disappearing.
"It was synergies between prairie dogs and bison, the two of them working together, that allowed the Great Plains to be the breadbasket of North America. Take away that foundational species and everything begins to collapse."
These days, more than 50,000 bison roam the Turner ranches. It's thought to be the biggest private herd in the world, and at least a tenth of all the bison in the US.
Turner drew criticism in 2010 when he offered to temporarily care for quarantined bison from Yellowstone National Park, in return for being allowed to keep most of their offspring. Opponents filed a lawsuit arguing that Yellowstone Bison should not be kept on private land, but a judged dismissed the challenge.
The species has made a remarkable recovery, thanks in part to Turner. On his land, they're accompanied by elk, mule deer, antelopes, wolves, bears, mountain lions, bobcats, coyotes, foxes, eagles and osprey.
The idea of Turner as a hands-on conservationist, riding on horseback across the restored wilds of Montana might jar with his public image as an outspoken, and sometimes controversial, mogul, but he has a long held love of nature.
He grew up on the plantations owned by his father, who ran a successful billboard company. In his youth, Turner loved to fish and to sail, but he had a difficult upbringing. His father beat him, and his sister died when she was a teenager. Turner found solace in nature, says Fonda.
According to those who know him, his relentless ambition is in part a quest for the approval of his father, who killed himself when Turner was 24.
"As Jane Fonda has said, what drives Ted Turner forward every single day, and trying to do good by the world and do good by his own family, is the fact that he knows at some basic level that he can save himself," says Todd Wilkinson, an environmental journalist and author of the book "Last Stand: Ted Turner's Quest to Save a Troubled Planet."
"And by trying to do good by the world, that makes the pain that he feels a little less," adds Wilkinson.
As Turner grew older, that childhood passion for nature was informed by a growing awareness of the perils facing our planet. His journey into conservationism came partly from a developing friendship with the great French underwater filmmaker Jacques Cousteau.
"The one person who looms largest in Ted Turner's life as a hero was the late Jacques Cousteau," says Wilkinson. "They shared a love for the ocean, they had difficult relationships with their own fathers, and Ted had seen Cousteau's documentaries."
Wilkinson recounts how, in the early 1980s, Turner and his sons stayed on Cousteau's boat in the Amazon. One night, Cousteau told Turner about the litany of environmental problems that he had seen in his travels: the first signs of dead zones in the Gulf of Mexico, ocean pollution, overfishing, and early evidence of coral reefs dying.
"Ted said, 'Well, this is overwhelming. I don't know what we can do,'" says Wilkinson. "And Cousteau said, 'Ted, what can men of good conscience do? If they know the world's going to end, they must do everything they can to prevent that from happening.'"
According to Wilkinson, when Turner returned from the Amazon he initiated CNN's first environmental reporting division, pushed for the channel to air more environmental documentaries, and became increasingly committed to philanthropy.
In the 1990s Turner bought more ranch land, re-introduced bison and set up the environment-focused Turner Foundation, as well as the Turner Biodiversity Divisions and the Turner Endangered Species Fund (TESF).
"The Turner Endangered Species Fund is all about a practical solution to a big problem, which is the extinction crisis," says Mike Phillips, who helped found the organization. "It's easy to say there's a problem, but can you back that up with an offering of a solution? Ted has always done that.
"Every time I talked to Ted I was seduced by his enthusiasm and his sincerity and the belief that Team Turner could show that private lands and private assets could make a substantive difference on behalf of endangered and threatened species," he says. "And that's the foundation on which the TESF is based."
But at the start of the Millennium, Turner's life was turned upside down by events from his personal and business life.
In the 1990s, his Turner Broadcasting System had merged with Time Warner, with Ted heading up their cable networks division. In 2000, Time Warner joined with AOL, and Ted Turner lost control of Turner Broadcasting.
Around the same time, he and Fonda separated, and later divorced.
He was devastated, and for a while, he was adrift.
But ultimately, without the distractions of work, Turner was left to focus even more on his environmentalism.
He developed his ranches by pioneering "eco-capitalism" -- the idea of using the free market to promote sustainability. Philanthropy aside, Wilkinson explains that Turner's view is that "conservation, if it's going to endure, has to pay for itself, especially if it's happening on private land."
The bison reared on Turner's ranches are sold for meat, some of it through his "Ted's Montana Grill" chain of restaurants. Again, it's that combination of idealism and pragmatism.
"He knew that he wanted to bring back the bison and he knew that to do it to scale, bison have to have an economic place in our system," says Fonda. "We had to learn to eat bison meat ... you couldn't just bring them back as a sort of exotic former main species. There had to be a reason, otherwise it wasn't going to happen."
Turner's ranches also generate income through eco-tourism, fishing and hunting. But making money is no longer a priority for Turner. These days, he is happiest just spending time on his flourishing Montana ranches.
A few years ago he was diagnosed with Lewy Body Dementia, a condition that causes him extreme fatigue and impairs his short-term memory.
"It exhausts you. Your stamina goes down," he explains. "You have dementia, you forget a lot."
"It's painful to watch somebody that's been so healthy and vibrant and active for the nearly six decades that I've known him, it's just really hard for me to see him decline," says his daughter Laura Turner Seydel.
"But I think dad is doing great," she adds. "I mean, he's 80 years old. He gets up and does yoga in the morning, goes out and gets on a horse and rides, goes out and gets in a stream and fishes -- who does that?"
After a lifetime of conservation work and philanthropy, Wilkinson is not alone in suggesting Turner deserves a Nobel Prize. But as well as the millions of acres of land he has restored and the countless species he has protected, he will leave another legacy: inspiring a new generation of environmentalists.
Recognizing the power of the media to educate about environmental issues, in 1990 Turner created the Captain Planet cartoon. It's the story of a green-mulleted superhero who fights eco villains, protecting the earth from environmental disaster. Its 113 episodes have been shown in more than 100 countries, translated into in 23 languages.
"Today we have untold numbers of young people who will say they were influenced by Captain Planet," says Wilkinson.
It's no coincidence that Captain Planet has five Planeteer sidekicks -- one for each of Turner's children, who have all grown up to be committed environmentalists.
Turner Seydel chairs the Captain Planet Foundation, which promotes environmental education projects around the world. "For over 28 years now, we've impacted over 10 million youth," she says. "Kids are learning to recycle. They're learning about renewable energy, they're learning about endangered species.
"Youth around the world that have really found their voice and are making a difference, like Greta Thunberg, and this is really a dream come true for dad, where youth are taking a really important leadership role in being part of the solution."
Environmentalist and former US Vice President Al Gore is a long-time friend of Turner's. "I think that the number of people that he has inspired in his life will be a fundamental part of his legacy," he says. "They will carry on the kind of work that he has always felt was so important."
If the five cartoon Planeteers are inspired by Turner's children, then Captain Planet himself is perhaps also a thinly disguised version of a real person with a mission to save the world.
"In terms of the body of his work... I defy you to find an individual that on his or her own has done more for humanity with a focus on the environment than Ted Turner," says Philips. "He is Captain Planet."
But Turner himself doesn't speak of a legacy. Walking among the magnificent bison that roam unimpeded on his treasured Montana ranch land, he believes his work is not yet done.
"I'm not patting myself on the back yet," he says. "We haven't saved everything yet. When we've saved everything, then I'll celebrate."