Ukraine: Key players

Yanukovych, the Ukrainian president, had maintained throughout 2013 that he wanted to sign an agreement to get closer to the European Union, then reversed course at the last minute after an unpublicized eight-hour meeting with Russian President Vladimir Putin. Yanukovych, from the industrial eastern heartland of Donetsk, served time in prison in the Soviet era for assault. As president, he has showered his immediate circle of Donetsk cronies with favors. Protesters have said they won't leave the Maidan, or Independence Square, in Kiev, Ukraine's capital, until he's out of the presidency.

Yatsenyuk is the leader of the parliamentary faction of the Fatherland Party, which was founded by Yulia Tymoshenko, the former prime minister who is now in prison. Yatsenyuk, an economist and lawyer, has always cast himself as a principled reformer and at times was at odds with Tymoshenko over questions of policy and politics. On a leaked call, Victoria Nuland, the U.S. assistant secretary of state in the Bureau of European and Eurasian Affairs, said she believed that Yatsenyuk was the protest leader with the most economic and governing experience.

The former WBO and WBC heavyweight champion had a knockout-to-bout ratio second only to Rocky Marciano's. Now he's in politics, and his party is called UDAR, which means "punch." Klitschko has no association with the Orange Revolution or the unpopular governments that followed it, but he is a ferocious critic of Yanukovych.

The head of the nationalist Svoboda party. Yanukovych did not offer him a position in the government in January. Tiahnybok credited the emergence of fanatical and often nationalistic soccer supporters for a change in Yanukovych's tone since then.

Ukraine's parliament Friday voted to free Tymoshenko, who has spent more than two years in jail on charges of abuse of office. The European Union, citing "selective justice," had demanded that she be released, but Yanukovych couldn't bring himself to do it. Wildly popular when she dramatically became the personification of the Orange Revolution nine years ago, her two stints as prime minister were troubled and complicated. Her supporters are passionate. So are her detractors.

The Verkhovna Rada on Friday voted for a return to the 2004 constitution, which gives the parliament, not the president, the power to pick the prime minister and most of the cabinet. It gives the prime minister — a post that has been vacant since Mykola Azarov resigned Jan. 28 — most of the power to run the government. The Rada is a unicameral body with 450 seats, 442 of which are currently filled.

Riot police called Berkut, which operate under the Interior Ministry and are descended from an elite force in Soviet times, have taken the lead in the clashes. On Friday, the Rada voted to remove the interior minister, who was blamed for violence against the protesters.