Dr Paul advocates free markets, low taxes and small government

But over the course of his campaign, this has changed - largely as a result of his cultivation of an online support base of a fervour unrivalled by any other candidate.

And while he is not regarded as a front-runner for the Republican nomination, Dr Paul has certainly made more of an impression at the polls than pundits ever expected.

He came second in the Nevada Republican caucuses on 19 January 2008, with 14% of the vote to winner Mitt Romney's 51%. (The two were the only candidates seriously to campaign in the state.)

The 72-year-old libertarian also did better than high-profile rival and former New York Mayor Rudy Giuliani in both Iowa and Michigan.

And, after achieving only 1% to 2% support in national polls through most of 2007, he appeared to be on an upward trend going into 2008, heading towards 5% in mid-January.

Facebook 'friends'

Analysts attribute his rising support to his huge online presence, as well as his plain-speaking performances in televised presidential debates.

Dr Paul's supporters have been campaigning online and on the ground

His dedicated, web-savvy supporters, who comb the internet for references to him and expend large amounts of effort trying to raise his profile, have become known as Paulites or Paulistas.

The candidate's videos are the most watched on the internet and he can claim more supporters on popular social networking sites MySpace and Facebook than any of his Republican rivals.

Among the practical successes the Paulites can claim is collecting almost $6m in 24 hours in December 2007, in an online fundraising drive that attracted more than 50,000 donors, half of them new.

Those funds helped Dr Paul spend money on TV advertising and campaigning in early primary states that he could only have dreamed of a year earlier.

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Dr Paul's campaign manager, Ken Snyder, pointed out after the Michigan primary on 15 January that the Texas congressman had outperformed expectations.

"After beating Rudy Giuliani in Iowa, and Fred Thompson in New Hampshire, Ron Paul has now bested both 'national frontrunners' in Michigan," he said.

"If I had predicted that result when this campaign started almost 12 months ago, I would have been laughed out of the room by the so-called experts."

One of the few hiccups in recent months has been an article in The New Republic magazine examining the publication of newsletters under Ron Paul's name in the 1980s and 1990s in which racist, anti-Semitic and homophobic views were expressed.

Dr Paul responded with a statement saying: "The quotations... are not mine and do not represent what I believe or have ever believed."

He added: "For over a decade, I have publicly taken moral responsibility for not paying closer attention to what went out under my name."

Anti-war stance

Throughout his years in Congress - first in the late 1970s and early 1980s, and more recently since 1997 - Dr Paul has been known for his adherence to strict libertarian principles.

Supporter Aaron Jones praises Dr Paul for his ideas and humility

His commitment to a limited constitutional government, low taxes and free markets has earned him the nickname Dr No, for his habit of voting against any legislation he sees as encroaching on those ideals.

He has consistently opposed the war in Iraq, on the grounds that the US should not entangle itself in the affairs of other nations or go to war without the approval of Congress.

That stance - which sets him apart from his Republican rivals for the presidency - has won him the backing of many anti-war activists, particularly among the younger generation.

Many also admire his dedication to the US Constitution and his message of personal freedom and responsibility.

Aaron Jones, a 29-year-old supporter from Indiana who was playing the guitar and handing out pocket copies of the Constitution by a polling station in New Hampshire, said he had been impressed by Dr Paul's selflessness.

"Ron Paul really stands against the establishment in so many issues," he said. "I've never met a more humble politician."

Delivering babies

Born and raised in Pennsylvania, Dr Paul completed medical school and served as a flight surgeon in the US Air Force during the 1960s.

He moved to Texas in 1968 and, around his political career, worked there as an obstetrician for years, delivering more than 4,000 babies before largely retiring from medical practice in 1996. He is opposed to abortion.

Dr Paul ran as the Libertarian Party's candidate for the presidency in 1988.

Having been re-elected to Congress in 1997, he currently serves on the House Committee on Financial Services and the House Committee on Foreign Affairs.

He and his wife, Carol, have five children and 17 grandchildren.