Yanukovych faced protests and calls for his resignation since refusing a partnership agreement with the European Union in November 2013. The president rejected the EU deal — which he had earlier agreed to in principle — because he said it would threaten the country's close trade ties with Russia.
As the movement grew and eventually became violent, Yanukovych introduced controversial anti-protest laws (later annulled) and took a short sick leave.
Under intense international pressure to end the violence, Yanukovych and opposition leaders signed a deal on Feb. 21 to allow early elections, a new constitution and new unity government. However, parliament quickly voted to depose Yanukovych, who fled Kyiv. The interim government issued an arrest warrant for Yanukovych, accusing him of "mass killings" of protesters. Yanukovych resurfaced in Russia and said he planned to continue to fight for Ukraine.
Klitschko, nicknamed "Dr. Ironfist," leads the Ukrainian Democratic Alliance for Reforms (UDAR). Klitschko, a former world heavyweight boxing champion, criticized President Viktor Yanukovych's handling of the EU deal, saying the people had been duped.
"Yanukovych doesn't want change," Klitschko, 42, told the Guardian. "He says he does. But he says he wanted European integration and that turned out to be a con." A prominent presence in the protest movement, Klitschko is seen as a likely potential successor to Yanukovych. He has confirmed he plans on running for president in 2015.
READ MORE: Vitali Klitschko leaving boxing for politics
Tymoshenko, the former prime minister who was narrowly defeated by Yanukovych in the 2010 presidential election, was freed from jail by the Ukrainian parliament's decree in February 2014.
Tymoshenko, leader of the Fatherland coalition, was found guilty in 2011 of abuse of office when she signed a gas deal with Russia. International observers deemed the verdict to be driven by political motivation.
She announced on March 27 that she will run in the May 25 presidential election.
READ MORE: Ukraine's Tymoshenko given 7 years in jail
Oleg Tyagnibok, leader of the nationalist and far-right Svoboda or "Freedom" party, also called for Yanukovych's resignation. Svoboda, Ukraine's fourth-largest party, rejects alliances with both Russia and the EU in favour of greater Ukrainian independence.
Svoboda has been criticized as being both xenophobic and anti-Semitic — a charge that Tyagnibok denies. Thousands of Svoboda protesters participated in a torch-lit march through Kiev in January 2014, shouting "Glory to Ukraine". The demonstration was held in honour of a Second World War partisan leader named Stepan Bandera. Eastern Ukrainians have maintained that Bandera cooperated with the Nazis — though citizens in the western region of the country view him as a national hero, according to the BBC.
Ukraine approved Yatsenyuk as the country's new prime minister in late February. Yatsenyuk, leader of the country's second largest party, Fatherland, in February 2014 rejected an offer to become prime minister in a coalition government with President Viktor Yanukovych.
Yatsenyuk said he would only consider the political alliance if the president made concessions, including constitutional reform. Yatsenyuk maintains close ties with the now-freed Yulia Tymoshenko.
U.S. President Barack Obama hosted Yatsenyuk at the White House on March 12. The meeting was seen as a diplomatic shot at Russia, as well as a major sign of the West's support of the new government.
Parliament granted temporary presidential powers to its speaker, Turchinov, shortly after President Yanukovych fled Kyiv. The legitimacy of that decision was unclear.
A close ally of former prime minister Yulia Tymoshenko, Turchinov has called for the formation of a unity government as soon as possible. He said top priorities include saving the economy and "returning to the path of European integration," according to news agencies.
Lutsenko, who served as Yulia Tymoshenko's interior minister, was imprisoned for abuse of office and embezzlement in 2012. His sentence was criticized as being politically motivated and after lobbying from the European Union, he was later released and pardoned. Lutsenko now leads the protest group known as the Third Ukrainian Republic.
The far-right, nationalist group dubbed the Right Sector, have deemed the current political crisis as an occasion to "destroy the state skeleton" in favour of a new order, according to the BBC.
The group, composed largely of young men, rejects joining the EU but is also similarly against building close ties with Russia. Right Sector demonstrators often wear masks and helmets and have led some of the most violent confrontations with riot police in Kyiv's Independence Square.
Zamana, the head of Ukraine's armed forces, was ousted from his post by presidential decree on Feb. 19. His replacement was the commander of the navy, Yurii Baidak. No reason was immediately given for the change.
READ MORE: Yanukovych names new army chief
Activist Dmytro Bulatov, 35, disappeared on January 22. He resurfaced eight days later and said he had been abducted and tortured by people with Russian accents.
Bulatov, leader of the AutoMaidan protest group, was bruised and cut. Part of his ear had been severed and he said his captors had pounded nails into his hands before abandoning him in a forest.
Two other violent kidnappings have similarly gripped Ukraine. Yuri Verbitsky and Igor Lutsenko were kidnapped from a hospital and were separated and beaten. Lutsenko was eventually freed but Verbitsky died, his body found in a forest.
Chornovol, a pro-opposition journalist who works for the online publication Ukrainska Pravda, was beaten and left in a ditch on Dec. 25, 2013. Chornovol has accused President Viktor Yanukovych of having orchestrated the attack in retaliation for critical articles she has written about the president. "For the last three years I have seen myself not as a journalist but as a person fighting Viktor Yanukovych," Chornovol told Deutsche Welle in January 2014.