Italian mountaineer Reinhold Messner is perhaps one of the world's last great adventurers: he has conquered the planet's highest peaks, crossed Antarctica and hunted for the elusive Yeti.

That he has lived to tell those tales, is mainly down to luck, he says.

Now 73 years old with an unruly mop of grey hair and a full beard, the man who counts German Chancellor Angela Merkel as a walking buddy says he is always in pursuit of the next challenge.

"Life is about daring to carry out your ideas," he told AFP in an interview at this week's Frankfurt book fair.

"And for me, it always comes back to the wilderness, nature, mountains."

One of the best-known living mountaineers, Messner became the first person to climb Mount Everest solo and without the help of bottled oxygen in 1980.

He also became, in 1986, the first the scale the world's 14 summits over 8,000 metres (26,000 feet), again without supplemental oxygen.

Along the way, he has pioneered an extreme style of mountaineering known as alpinism, where climbers aim to reach the top with as little material and outside help as possible.

"We were the first generation to say: we don't need all that," recalls Messner, who grew up in South Tyrol and started climbing at the age of five.

But it is an art that is increasingly getting lost, he says, dismissing today's climbers who rely on sherpas and ready-made routes to reach the peak.

"The true alpinist doesn't want any infrastructure, he wants to go into the wild.

"And the odds of getting killed there are relatively high. And most people are sensible enough not to want that," he laughs.

"But the art of not getting killed is only an art if there's a chance you could die," he adds. "If I rule out the chance of getting killed in advance, the whole thing becomes a game, or tourism or consumerism."

Tragedy

Messner's own exploits have not been spared from tragedy.

In 1970, his brother Guenther died as they were descending Pakistan's "killer mountain" Nanga Parbat in bad weather. Messner himself lost seven toes to frostbite.

His brother's death prompted one of the most infamous rows in mountaineering history, which haunted Messner for decades.

Other members in the expedition accused him of leaving his brother behind near the summit in a bid to become the first to ascend the mountain from one side and descent from the other.

Mount Everest

Mount Everest is considered one of the toughest mountains to climb
It wasn't until 2005 that Messner said he felt vindicated, when Guenther's remains were recovered close to where he always insisted his brother had died in an avalanche.

His daring feats have become the stuff of legend, but Messner -- who has a history of falling out with teammates and preferring to climb alone -- says he has experienced plenty of failures along the way too.

"Around half of the top alpinists have died climbing," he said.

"Of course if I'm careful and turn back more often than the others, I can increase my chances of survival. But if I hadn't been lucky a few times, I wouldn't be here."

Walking with Merkel

Messner later moved on to different challenges, crossing the Gobi Desert and Antarctica, and claims that he discovered that the Yeti, also known as the "Abominable Snowman", was just a bear.

A celebrity in his home country, he then went into politics. Running as an independent, he served as a member of the European Parliament for five years from 1999, sitting with the Greens.

Messner, who is married and has four children, then went on to found a series of mountain-top museums to raise awareness about conservation.

He is also a prolific writer and was in Frankfurt to present his latest book "Wild", chronicling the true story of an ill-fated 1916 Antarctic expedition.

He still climbs mountains today, though no longer the behemoths of the past.

A longtime friend of Merkel, he regularly accompanies Europe's most powerful woman on walks during her summer holidays in the Alps.

"She's an incredibly tough woman. She has no time for training... but she has a tenaciousness that I very much admire. And she has no vanity."

Today, Messner spends his time making films and talks excitedly about his current one, which is set in Kenya and tells the story of two climbers who run into trouble and are faced with life-altering dilemmas.

"I want to observe how people act in a very difficult situation," he says.

After a lifetime of seeking out the next frontier, he believes filmmaking will be his final project.

"I figure I need about five years to learn how to do this right, then another five years to make good movies. After that, I know I won't have any more energy left."

He says he has always known when the time was right to move on to the next chapter.

"I was always at my best when I was learning, when I was curious. When I had yet to see past the next horizon."