KIEV, Ukraine - Towering over his fellow protest leaders, Vitali Klitschko, the reigning world heavyweight boxing champion, has emerged as Ukraine's most popular opposition figure and has ambitions to become its next president.

Thanks to his sports-hero status and reputation as a pro-Western politician untainted by Ukraine's frequent corruption scandals, the 6-foot-7 Klitschko has surpassed jailed former Prime Minister Yulia Tymoshenko in opinion polls.

As antigovernment demonstrations continue to grip Ukraine, the 42-year-old boxer-turned-politician is urging his countrymen to continue their fight to turn this ex-Soviet republic into a genuine Western democracy.

"This is not a revolution. It is a peaceful protest that demands justice," Klitschko told the Associated Press on Wednesday. "The people are not defending political interests. They are defending the idea of living in a civilized country."

Dubbed Dr. Ironfist for his prowess in the ring, he has 45 wins in 47 fights, 41 by knockout. He has defended his title 11 times, most recently in September 2012, and plans to have one more bout before he retires. He still spends several hours a day training.

Now he must prove his stamina in the political arena.

Despite earning a doctorate in sports science, Klitschko has had to fight a stereotype of being intellectually unfit to run this nation of 46 million.

Having been raised - like many Ukrainians - in a Russian-speaking family, Klitschko only recently learned Ukrainian and sometimes struggles to find the right word. Still, he appeals to many Ukrainians with his air of sincerity and his image as a handsome tough guy ready to defend his compatriots.

"He is a national hero and comes across as being decent," said Andreas Umland, assistant professor of European studies at the Kyiv Mohyla Academy.

Klitschko was one of only a few opposition politicians who tried to stop several hundred radical protesters from storming President Viktor Yanukovych's office during a demonstration Sunday that drew hundreds of thousands to the streets of the capital, Kiev.

As the boxer called for peace, the jubilant crowd chanted his name. Beside him stood his wife, Natalia, a former model who recently launched a singing career. The couple have three children.

The angry protests were sparked by the president's abrupt decision last month to ditch a political and economic treaty with the 28-nation European Union in favor of closer economic ties with Russia, which had threatened Ukraine with trade consequences if the country signed the EU deal.

On Wednesday, Klitschko's party joined two other opposition parties in blockading the Ukrainian parliament as part of a nationwide strike.

Klitschko has kept his two careers separate - never joining other lawmakers in the frequent brawls that have marred parliament. "Physical force plays no role in politics," he said. "The power of thought is much stronger."

How good are Ukrainian lawmakers at throwing punches?

"If you judge this from the standpoint of [my] profession, they don't have any talent," he said.