KIEV, Ukraine — On a Sunday in December when the Ukrainian uprising seemed about to tip into wide-scale violence, Petro Poroshenko, a pro-Western billionaire, thrust himself between antigovernment protesters and riot police officers clashing outside the presidential headquarters, climbed on a bulldozer that was threatening to plow through the crowd and grabbed an orange plastic megaphone.

“Friends, calm down,” he shouted, as pro-government thugs brought in to antagonize the demonstrators cursed him and hurled anti-Semitic slurs, though he is a member of the Ukrainian Orthodox faith, not Jewish. As chaos swirled, Mr. Poroshenko, 48, stood his ground, helping keep injuries to a minimum, but also cementing his status as a leader of the pro-European opposition and defying the stereotype of the superrich above it all.

Now, with less than a week to go until a presidential election here, Mr. Poroshenko is once again at the center of a fracas that most of his fellow oligarchs would rather avoid. The latest polls show Mr. Poroshenko, a confection magnate known as the Chocolate King, as the heavy favorite, likely to avoid a runoff with his strongest opponent, former Prime Minister Yulia V. Tymoshenko. Ms. Tymoshenko insists that the polls are wrong and that she will surge ahead.

A poll by the Kiev International Institute of Sociology, conducted April 29 to May 11, found Mr. Poroshenko supported by 34 percent of all voters, compared with 6 percent for Ms. Tymoshenko and 4 percent for Sergey Tigipko, a member of Parliament and former economics minister; 25 percent said they were undecided. The survey had a margin of sampling error of plus or minus three percentage points.