KIEV, May 24 (Reuters) - Ukrainians will vote for a new president on Sunday but the election faces disruption in eastern regions of the former Soviet republic where pro-Russian separatists have seized strategic points in several cities.
The election was called after pro-Europe mass street protests forced Ukraine's Moscow-backed president Viktor Yanukovich out of office in February. He then fled to Russia.
Kiev's pro-Western interim government hopes the election will restore political stability after five months of upheaval which has also included Russia's annexation of Ukraine's Black Sea peninsula of Crimea.
Here are pen portraits of the leading candidates from a field of 21 who have registered for the May 25 vote.
If no candidate gets more than 50 percent in the first round of voting on May 25, there will be a run-off vote between the two leading contenders on June 15.
* PETRO POROSHENKO (48)
Poroshenko, a confectionery tycoon, is the front runner in the race, with some opinion surveys indicating he may even win outright in the first round.
He was the only Ukrainian oligarch to move swiftly to support the popular uprising against Yanukovich which began in central Kiev in late November, devoting his '5th Channel' TV station to coverage of the protests.
A seasoned politician who served as foreign minister and economy minister in previous administrations, he owns a chain of confectionery shops that have put the billionaire on Ukraine's top 10 rich list, earning him the nickname "Chocolate King".
Poroshenko, whose chocolate manufacturer Roshen is one of the world's top 20 confectionery firms, backs Ukraine's integration with the West and his business has been targeted by Russia.
* YULIA TYMOSHENKO (53)
Born in Ukraine's industrial east, Tymoshenko was Ukraine's prime minister for a short stint in 2005 and then from late 2007 till 2010, when Yanukovich beat her in a bitter run-off vote for the presidency. Brought to power by pro-Western street protests known as the Orange Revolution, her time in office was marked by bitter infighting involving her erstwhile Orange ally Viktor Yushchenko who had become president.
Wearing a peasant-style hair braid that became her trademark and with strong organisational powers, Tymoshenko, a fiery public speaker, became a force in Ukrainian politics. But she was dogged by involvement in gas deals in the 1990s from which she made a fortune and which gave her the nickname of "gas princess". Seen by many as divisive and too sharp of tongue, she can inspire loathing as well as loyalty among Ukrainians.
Tymoshenko was convicted and jailed for 2-1/2 years under Yanukovich for abuse of office, walking free only in February when her nemesis fled to Russia. But with the dynamics of the political establishment drastically changed by the Maidan revolution, she has failed to re-kindle her old strong support.
Surveys put her in a distant second place.
* SERHIY TIGIPKO (54)
Tigipko is a banker and parliamentary deputy who has served in several governments, once as economy minister, and was at one time close to the ousted Yanukovich, serving as his campaign director for a short while in late 2004.
Seen as the third-placed candidate in opinion polls, Tigipko, whose main voting base is in the Russian-speaking east, is highly critical of Kiev's interim authorities for the way they have handled separatist rebellions there.
He says Kiev has not done enough to build bridges with people in the east or addressed legitimate grievances, particularly over Russian language rights, thereby opening up a space for the pro-Moscow separatists.
* MYKHAILO DOBKIN (44)
Dobkin, a businessman and former governor of the eastern city and region of Kharkiv, is the official candidate of the Party of Regions, once Ukraine's ruling party led by Yanukovich.
He fiercely criticised the pro-Europe street protests in Kiev and has questioned the legitimacy of Ukraine's interim government, but the expected disruption of Sunday's election in the eastern regions is likely to eat into his support.
His election campaign has been financed by Ukraine's richest man, coal and steel magnate Rinat Akhmetov, who has belatedly condemned the actions of the pro-Russian separatists and called on people in eastern Ukraine to retake control of their cities.
Dobkin is on a list of nearly 30 Ukrainians - also including Yanukovich - whose assets have been frozen by Switzerland over their role in the Ukraine crisis. (Compiled by Gabriela Baczynska and Richard Balmforth; Editing by Gareth Jones and David Evans)