As the boxer called for peace, the jubilant crowd chanted his name.
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 after several years of preparations and to focus on ties with Russia instead. Russia has been threatening Ukraine with economic trading consequences if the country signed the EU deal.
The demonstrations in Kiev were galvanized when the Yanukovych's government sent in riot police with truncheons to break up a small, peaceful rally in the middle of the night, injuring dozens.
"They took away people's hope to implement reforms, to change the situation in the country," Klitschko said. "They stole our hope."
Now Klitschko must prove that his political stamina is equal to that he displayed in the boxing ring. In more than 15 years as a professional boxer, Klitschko has scored 45 victories in 47 fights, 41 on them with knockouts, earning the nickname "Dr. Ironfist." He plans to have one more bout before he retires and still spends several hours a day training.
Despite earning a doctorate in sports science, Klitschko has had to fight a stereotype of being intellectually unfit to run this economically troubled, Texas-sized country of 46 million. Having been raised in a Russian-speaking family, Klitschko just recently learned Ukrainian and sometimes struggles to find the right word. But at the same time, he appeals to many Ukrainians, with his air of sincerity and his image of 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 made his first foray into politics during the country's 2004 Orange Revolution, the mass protests that led to the annulment of Yanukovych's fraud-tainted presidential victory and ushered in a pro-Western government. After winning a fight in the United States, Klitschko flew to Kiev and appeared in the heart of those protests wearing an orange scarf, the symbol of the revolution.
Next to him stood his brother, Wladimir Klitschko, now 37, a heavyweight world boxing champion in a parallel boxing organisation who is engaged to the American actress Hayden Panettiere, star of the TV series "Nashville."
Vitali Klitschko has three children with his wife, Natalia, a former model who recently started a singing career.
After two failed attempts to be elected mayor of Kiev, Klitschko entered national politics last year when his pro-Western party - aptly named Udar (Punch in English) - finished a strong third in the parliamentary election running on a reform and anti-corruption platform. He was able to capitalise on popular anger with Yanukovych, who is accused of putting Ukraine on an authoritarian path, and with voters' disillusionment with the Orange leaders, now in opposition, including Tymoshenko.
A year before the 2012 election, Tymoshenko was jailed for abuse of office, charges the West considers politically motivated. The pro-Western Tymoshenko has been Yanukovych's biggest political rival for years.
Klitschko's mother was a school teacher and his father an army pilot whose job took him to remote military bases across the Soviet Union and Eastern Europe. Klitschko was born in 1971 in Kyrgyzstan, then part of the Soviet Union.
He said he embraced Western values while training in Germany and the United States for matches, and he wants to bring those values home to Ukraine.
"Those people who are in politics (now) do not make it their goal to change the country," Klitschko said, towering over an AP reporter at 2 metres. "They are simply plundering the country."
Unlike many Ukrainian politicians and businessmen who are accused of making their fortunes in shady privatization deals and business wars in the tumultuous post-Soviet years, Klitschko's millions come from a transparent source - the boxing ring.
An opinion poll in September predicted that Klitschko would get 15.5 percent of the votes in the first round of a presidential election, compared to Tymoshenko's 13.2 percent. Yanukovych would get 19 percent, but he would lose to Klitschko in a run-off, according to the Razumkov Center poll of 2,010 respondents. It had a margin of error of 2.3 percentage points.
In October, Klitschko announced that he would run for the presidency in early 2015, even though parliament, dominated by Yanukovych's allies, passed a law that sought to bar Klitschko from running on the grounds that he had spent several years in Germany and paid taxes there.
Klitschko was appalled, calling Ukrainian politics a dirty business, unlike anything he had seen in boxing.
"It's impossible to compare them because in boxing there are rules, in Ukrainian politics the rules are absent," Klitschko said.
One thing the boxer has never done - join other Ukrainian lawmakers in the frequent bloody fights that have marred parliament in recent years.
"Physical force plays no role in politics; the power of thought is much stronger," Klitschko said.
How good are Ukrainian lawmakers at throwing punches, anyway?
"If you judge this from the standpoint of (my) profession, they don't have any talent," Klitschko said.
- AP
