(CNN) -- As developments continue to unfold rapidly in Ukraine, the key players in the unrest are making moves. Here are brief profiles to explain who's who in the crisis:
President Viktor Yanukovych
President Yanukovych remains defiant in the face of calls for him to resign, despite a unanimous parliamentary vote to remove him from office. It's not clear if the vote carries any legal weight.
In a televised statement from the eastern city of Kharkiv, he said, "I am not trying to leave the country. I am not trying to resign. I am the elected President."
Earlier, his absence from the capital, where his living quarters were emptied out, prompted rumors he might stand down or quit the country.
Yanukovych was elected President in 2010.
The wave of unrest in Ukraine began in November, when Yanukovych scrapped a European Union trade deal and turned toward Russia.
Opposition hit the streets about Yanukovych's backpedaling from the trade pact. That move and Russia's offer the following month to buy $15 billion in Ukrainian debt and slash the price Kiev pays for its gas played into the storyline of Ukraine being a proxy for battles between Russia and the West.
Another factor in Yanukovych's decision not to sign the deal is likely to have been the EU's demands that he release from jail former Prime Minister Yulia Tymoshenko, his political opponent. The Orange Revolution that swept then-prime minister Yanukovych out in 2004 also brought Tymoshenko to power.
Leading opposition leader Tymoshenko, 53, has been released from prison in Kharkiv, a spokeswoman for her Fatherland party said.
News of her release, nearly two-and-a-half years after she was jailed, came only hours after Ukraine's Parliament passed a resolution calling for her freedom.
Tymoshenko, who is a former Prime Minister, lost the 2010 presidential election to Viktor Yanukovych.
The following year, she was sentenced to seven years in prison after being convicted of abuse of authority over a natural gas deal negotiated with Russia in 2009.
She repeatedly called the trial a farce. The United States and Europe see the punishment as politically motivated.
In 2012, after Tymoshenko was allegedly beaten unconscious by guards, she went on a hunger strike to draw attention to "violence and lack of rights" in her country.
She is known as a hero of the country's 2004 revolution.
Another opposition leader is former world-class boxer Klitschko.
He has been the biggest and most well-known opposition figure during the crisis.
In a sign of his influence, it was Klitschko who went to Yanukovych's office for negotiation talks.
Klitschko heads the Ukrainian Democratic Alliance for Reforms party.
The embattled President offered Klitschko the post of deputy prime minister on humanitarian issues, which Klitschko turned down.
Yatsenyuk, 39, has led the opposition Batkivshchyna, or Fatherland, party, to which jailed former Prime Minister Yulia Tymoshenko belongs, since December 2012.
He can claim experience in government, having been chairman of Ukraine's parliament, the Verkhovna Rada, from 2007 to 2008, according to the website of his foundation, Open Ukraine.
Before that, he served as Ukraine's Foreign Minister in 2007 and as its Economy Minister from 2005 to 2006.
Speaking with CNN's Christiane Amanpour in December before the protests escalated into lethal confrontation, Yatsenyuk urged Yanukovych to compromise and outlined his own vision for reform.
Ukraine leaders need to deliver changes, he said, something the "corrupted government" and "corrupted president" have not done.
"People still believe in their future -- in their European future," he said. "I believe that we will definitely reach our target: a prosperous and pro-European country."
He turned down Yanukovych's offer of the post of Prime Minister in January.
Tyahnybok has headed the nationalist, far-right opposition party Svoboda, or Freedom, for the past decade.
According to the biography on his party website, his early views were shaped by the surveillance under which the Soviet security service, the KGB, kept his family, and his grandfather's oppression under Stalin.
He studied medicine at college while also completing his military service. He got involved in politics while a student and joined the Svoboda party in 1991.
Tyahnybok was first elected to a local council position in 1994, aged 25, and was elected to the parliament four years later. He became head of the party in 2004, when it changed its name from the Social National Party of Ukraine to Svoboda.
Concerns have been raised in some quarters about the extremist views allegedly held by some members of the party.
But in an interview with the New York Times in 2012, Tyahnybok denied that Svoboda was anti-Semitic, xenophobic, anti-Russian or anti-European. "Svoboda is simply and only a pro-Ukrainian party. And that's it," he is quoted as saying.