A two-time prime minister and a deputy prime minister for energy, Yulia Tymoshenko, was once known as the 'gas princess' for her designer clothes and involvement in the gas industry.
Ukraine will elect a president on Sunday, in what's seen as a three-way contest.
Volodymyr Zelenskiy, a television comedian is expected to win the first round.
But it may go to a run-off, and the other two main candidates are longstanding political rivals: the current President Petro Poroshenko, and former Prime Minister Yulia Tymoshenko.
Allegations of electoral fraud are already flying around, with Poroshenko and Tymoshenko trading accusations and Zelenskiy implying wrongdoing by his rivals via his jokes.
TRT World's Francis Collings reports from Kiev.
Here is a brief look at Tymoshenko's political career.
Known as the 'gas princess' for her designer clothes and involvement in the gas industry, Yulia Tymoshenko, then deputy prime minister for energy, was fired after charges of forgery and gas smuggling in her previous business were brought against her in 2001.
Tymoshenko spends a month in detention. She denies the charges as a political witchhunt and is later cleared by the courts.
She was later appointed as Ukraine's prime minister for the first time in 2005. In December 2007, the country's parliament voted in Tymoshenko as prime minister for a second stint.
Tymoshenko was defeated in the 2010 presidential elections and the next year sentenced to seven years in prison over her 2009 gas deal with Russia on charges of abuse of power. She was released from jail in 2014.