Ukraine's President is running against ... Vladimir Putin

Analysis by Nathan Hodge, CNN

Updated at 1019 GMT (1819 HKT) March 31, 2019

A woman casts her ballot at a polling station in Kiev during Sunday's election.

Kiev, Ukraine (CNN) — The front-runners in Ukraine's presidential election are a chocolate magnate, an energy tycoon-turned-populist and a television comedian. That may sound like a parody headline, but Sunday's vote is a serious business for a country at war.

Ukrainians are heading to the polls on Sunday after five years locked in a proxy war with Russia. In 2014, Russian troops annexed the Black Sea peninsula of Crimea, and Moscow fueled a separatist conflict in eastern Ukraine's Donbas region. The United Nations estimates that, as of February 15, the fighting has claimed almost 13,000 lives, with at least 3,321 civilian deaths and an estimated 9,500 combatants killed.

The incumbent, President Petro Poroshenko, is campaigning on his ability to play tough with Russia. In a statement this week on Twitter, Poroshenko cast Russian President Vladimir Putin as his main opponent.

"When asked who is my ally, with whom I am ready to unite and coordinate my actions, I answer: my ally is the Ukrainian people," he tweeted Tuesday. "Who is my opponent? I am not ashamed to say it openly -- this opponent is Putin."

Sunday's vote, however, may bring no clear outcome. If there is not an outright winner with an absolute majority of votes in the first round, the top two candidates go on to a second round on April 21.

Poroshenko faces an uphill battle to make it to that second round. Earlier this week, a poll by Rating Group Ukraine showed that the leading candidate, Volodymyr Zelensky, has the support of 27.7% of intended voters.

Just under a year ago, the President's support among likely voters was in the single digits. Since then, Poroshenko has reduced the gap: In another recent survey, American pollster GQR found the current president catching up with Zelensky, with 20% of likely voters saying they would vote for him if the election were held the coming Sunday.

Ukrainian comedian and presidential candidate Volodymyr Zelensky casts his ballot on Sunday.

Household name

Poroshenko, a tycoon best known for his ownership of chocolate manufacturer Roshen, may have the advantages of incumbency. But he's competing against someone who has major name recognition.

Zelensky is a comedian and the star of "Servant of the People," a Ukrainian television series now carried on Netflix.

And in a made-for-TV twist, the plot of the series foreshadowed his quixotic political bid: Zelensky plays a down-and-out schoolteacher who unexpectedly becomes President of Ukraine after becoming famous for an anti-corruption rant that goes viral on social media.

"Servant of the People" is, in effect, a campaign advertisement for Zelensky: A new episode airs on Wednesday on the 1+1 channel, just days before the election.

But political observers also say Zelensky is something of a blank slate, a complete newcomer to politics whose mastery of policy details is still rather scant.

Poroshenko, by contrast, has campaigned on a patriotic and national-security platform, running on a slogan of Armiya, Mova, Vira (meaning "army, language, faith.")

Poroshenko in recent months has stepped up confrontation with Russia. After Russia seized three Ukrainian navy ships and detained 24 sailors in a strategic waterway that links the Azov Sea with the Black Sea in November, Poroshenko's government responded by imposing martial law and warning of impending Russian invasion.

Ukraine's incumbent President has also played on Ukraine's bid for greater spiritual independence from Russia, welcoming a decision last October by Bartholomew I of Constantinople, the spiritual and symbolic leader of the eastern Orthodox church, to recognize an independent Ukrainian Orthodox Church.

Yulia Tymoshenko came to power in the wake of the Orange Revolution but was later jailed over a natural gas deal.