Miami (CNN)Yuri Gagarin showed him how to reach for the stars, but it was another intrepid traveler who set Wladimir Klitschko on the road to global domination.
Wladimir Klitschko: Iron Curtain no barrier for 'Dr. Steelhammer'
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Born in Soviet-era Kazakhstan, the boy who would become one of boxing's greatest champions had just one dream -- to see what the outside world had to offer.
Gagarin might have been the first man to journey into outer space, but Klitschko's real inspiration was Robinson Crusoe, the castaway title character of Daniel Defoe's classic 18th-century novel.
"I'd been reading this book so many times," Klitschko tells CNN's Human to Hero series.
"My motivation was to get out. I just wanted to see the world. You had to be a politician or an athlete to travel outside of the Soviet Union and to cross the border. As a regular citizen you couldn't make it. So I decided okay, I'm too young to be a politician, but for an athlete it's just perfect."
Klitschko, then in his early teens, had the perfect example of how to escape -- his older brother Vitali.
"Vitali, who is five years older, started with sports, and he went all over the world," explains Wladimir, who turned 39 at the end of March.
"He was coming back telling me stories, showing me pictures. I got really excited about it. So I was following in the footsteps of my brother to become an athlete, and eventually to become a champion."
They would both become boxing champions, dominating the heavyweight scene for the past decade -- often both holding various title belts -- before Vitali retired to take up a career in politics. But they would never step into a ring together.
"We are very competitive. It's something we have in our blood," Wladimir says. "Each of us want to show the other that he can do things better. But on the other hand there is a lot of respect and love to each other.
"We never competed against each other in any tournaments. We sparred with each other, and those sparring sessions were not fun. It was very bloody, emotional, and we just realized after getting injured, in another sparring session against your brother, we decided not to do that.
"It's something that we also promised our mother. She said you can box however you want, but promise me one thing, you will never fight each other in the ring."
It was the younger Klitschko who first came to worldwide prominence when he won the Olympic heavyweight gold medal in Atlanta in 1996, aged 20.
Vitali was excluded from Ukraine's first entry as an independent nation after testing positive for a banned steroid -- which he attributed to treatment for an injury.
"Those Olympic Games, and winning them, changed my life," says Wladimir, who competed in his brother's weight class.
"Suddenly I got all these invitations from the biggest promoters in the world."
The Klitschko family had moved to Ukraine, where father Vladimir was posted as part of his military career.
"My father was in service, and I changed seven schools, so there was a lot of traveling," says Wladimir.
"He taught my brother and me how to be disciplined. It takes a lot of discipline to continue for many, many years what you've been doing and actually not just being good. It's improvement. There is a big difference between being good and great."
The brothers lost their father to cancer in 2011, aged 64 -- the result, Wladimir says, of the major general's role in helping to clean up the Chernobyl nuclear plant after the power plant's meltdown 25 years earlier.
"A lot of his buddies passed away right away after that," Klitschko says. "He had such strong health, so he lasted for a long, long time but eventually it also got him. He passed away because of the consequences of the strategy in Chernobyl."
Vladimir was able to see his sons turn professional in late 1996. Having decided against working with boxing impresario Don King -- who has promoted some of the sport's greatest fighters -- they relocated to Germany, a country which has become their second home.
Both notched up an impressive string of victories to become title contenders, helped by the near-professional level of training they had while growing up.
"It was not a coincidence that I won a gold medal because I'd been competing for six years when I was at the Olympics," Klitschko says.
"I was competing a lot and I had a lot of experience and a lot of fights. Boxing was very popular in Soviet times, and amateur sport in general. It was traditional. So I got the best out of it."
In fact, the Klitschkos had very little exposure to professional boxing as children -- greats like Muhammad Ali, Sugar Ray Leonard and Tommy Hearns were people they'd hear about but not see in action.
Wladimir said his boxing education was taken to another level when he started working with famed trainer Emanuel Steward, who had actually stood in the opposite corner when Vitali lost to defending champion Lennox Lewis the previous year in 2003.
"He taught me to love the sport. I never was in love with the sport, which kind of sounds maybe not normal, even if I was practicing it," Klitschko says.
"I didn't know much about boxing, but through Emmanuel I got to learn and love the sport. Basically he shaped me into the form of a champion that I am today."
Next month, Klitschko will defend his WBA, IBF, WBO, IBO and Ring Magazine titles against unbeaten American Bryant Jennings.
It will be his fourth time at New York's iconic Madison Square Garden, the scene of some of boxing's greatest moments.
Since Lewis retired in 2004, the heavyweight division has increasingly lacked top-class contenders to topple the Klitschkos.
Vitali retired with a record of 45-2, having made nine successful defenses of his WBC title before relinquishing it.
Wladimir is 63-3 and has not been beaten since 2004, in his first fight under the late Steward's tutelage.
He attributes his success to his methodical preparation -- both brothers earned a PhD in Sports Science, lending weight to their nicknames of "Doctor Steelhammer" and "Dr. Ironfist" (Vitali).
"My training routine has been developed through the experience that I started with at 14," Klitschko says.
"It made me to create a system that works for athletes and works also for any other person who is not really involved in top sport but wants to stay fit and be fit. It's simple: Find a goal, be disciplined, and know the system."
The Klitschkos have been fighting for another system outside the ring: Democracy.
Vitali was a key opposition leader during last year's protests against Russia's invasion of Ukraine and subsequent annexation of Crimea. As mayor of Kiev, he is having to deal with the ongoing unrest which has split the country.
"It affects not just Ukraine, it's not a local conflict -- this is actually protection of the democracy that has been developed over hundreds of years in the Western world, and where Ukraine wants to go," Wladimir says.
"We want freedom. We have achieved many things in moving forward and showed to the world that we do not want to live in a dictatorship."
While Vitali has moved on to politics, Wladimir still has goals to achieve in boxing.
"I'm trying to unify the last belt that he held, the WBC belt," he says of the title, which is held by Deontay Wilder, the first American heavyweight champion since 2006.
His motto, which comes from the Cold War era, was first made famous by John F. Kennedy when, in 1961 -- six weeks after Gagarin's historic flight -- the President vowed that the U.S. would put a man on the moon before the end of the decade.
"Failure is not an option." It's emblazoned on his training clothes, and on the walls of the Miami gym where he is preparing for the April 25 bout with Jennings.
"There is only moving forwards and getting things done. And that's what I think about my opponent when I am in the ring," he says.
"Even if I'm maybe not the youngest fighter, when I see my opponent in a certain way, I see a reflection of myself. And I know exactly what my opponent is expecting from me, and I can read him very well, his body language, his mental strength or weakness.
"It's something that makes me excited because I do my homework. I prepare it in a very specific and systematic way. I have created a system which works very well. I definitely think that you, my opponent, have only one chance to leave this ring -- as a loser. There is no other option."
While Klitschko is not yet thinking of retirement, he has followed Vitali in starting a family.
Last December marked the arrival of baby daughter Kaya -- his first child with fiancée Hayden Panettiere.
At 6 foot 6 inches tall, he towers over the diminutive U.S. actress -- best known for roles in the TV series "Heroes" and "Nashville" -- but she has stood by his side during visits to Kiev during the recent unrest.
"I need to get used to being a father, which is really exciting. So I hope I'm going to have a big family with multiple kids in it," Klitschko says.
He hopes to be as much of a role model to his family as his own father was.
"I know that it's not just the presence of you in your children's life, but also being a good example with what you're doing and how you do things."
Failure is probably not an option.