David Cameron's supporters paint him as a principled but pragmatic politician with a huge capacity for quick thinking and grace under pressure.

Opponents depict the 48-year-old Conservative leader as a privileged smoothie who hates to break a sweat.

Cameron, who has been Britain's prime minister since 2010, is fighting for his political life in Thursday's election, which polls say is too close to call. If he fails to win a second term against Labour's Ed Miliband, he will almost certainly be dumped as Tory leader.

"I think he would be less devastated than most people, just because he is more of a human being than most politicians," said James Hanning, co-author of the biography "Cameron: Practically a Conservative."

Cameron is often depicted in the press as the prime minister who likes to "chillax." Observers have struggled to pinpoint what he believes in, and what has driven him to the top of British politics.

The son of a stockbroker, Cameron attended Eton, the country's most elite boarding school, which counts Princes William and Harry among its alumni.

At Oxford University, he studied politics, philosophy and economics and was a member of the Bullingdon Club, a rowdy dining-and-drinking society with a reputation for drunken vandalism.

After graduating, Cameron began work as a researcher for the Conservatives and rose quickly through the party, with a spell in PR for TV company Carlton Communications.

He was elected to Parliament in 2001 and chosen as party leader in 2005, when the Conservatives had lost three successive elections to Tony Blair's Labour. Cameron, another young modernizer, was branded the "heir to Blair" in the press.

In his first years as leader, he articulated a type of compassionate Conservatism, describing his vision of a "Big Society" built on neighborliness and volunteering. In government, he legalized same-sex marriage, despite the opposition of Tory traditionalists.

But his administration also slashed public spending to curb a deficit swollen by the 2008 banking crisis, and cut welfare benefits to some of the country's poorest people.

Many on the right wing of the Conservative Party mistrust Cameron's social liberalism, and consider him tainted by his failure to win the 2010 election outright against unpopular Labour leader Gordon Brown. Cameron had to put together a coalition with the Liberal Democrats in order to govern.

Cameron's re-election pitch is based primarily on the recovering British economy. Unemployment is falling, GDP is growing modestly and interest rates are low.

If voters back the Conservatives for financial security, Cameron will remain in 10 Downing St — although he has said he won't seek a third term.

If he's wrong, Hanning said, he'll go down in history "as the man who couldn't beat Gordon Brown or Ed Miliband. That's pretty bad."