Fred Thompson, a Hollywood actor and former senator, has said he intends to run for US president in 2008.
Former Tennessee Senator Fred Thompson is a successful actor
The 64-year-old, who joins a crowded field of Republican contenders, told newspaper USA Today about his campaign plans, after months of speculation.
He is already well known for his role as a district attorney in TV series Law & Order, and has been polling well.
Mr Thompson is expected to launch a "testing the waters" committee soon, a first step toward officially declaring.
The formal declaration of his candidacy could then come within weeks, with 4 July being rumoured as a possible date.
The former two-term senator for Tennessee has already been hiring staff, making speeches and establishing a strong internet presence.
'In the hunt'
Reports began circulating on Wednesday that he had decided to make official his informal but already attention-grabbing initiatives towards running for president.
"I can't remember exactly the point I said, 'I'm going to do this'," Mr Thompson told USA Today in an interview published on Thursday.
"But when I did, that thing that occurred to me: 'I'm going to tell people that I'm thinking about it and see what kind of reaction I get to it'."
He told the paper that his late start to campaigning carried "certain advantages", not least that his use of the internet "has allowed me to be in the hunt, so to speak, without spending a dime".
Observers say he could pose a threat to all three of the main contenders for the Republican nomination, Senator John McCain, former New York Mayor Rudolph Giuliani and former Massachusetts Governor Mitt Romney.
Some polls have put him at second or third place among potential Republican voters struggling to decide who to back in a field of almost a dozen candidates.
He has strong conservative credentials on issues such as gun control and abortion and, while he voted in 2002 to authorise the Iraq invasion, he is not as closely associated with the war as some of his rivals.
His charisma and ability to perform for the crowds are expected to stand him in good stead on the campaign trail.
Inevitably, parallels have been drawn between Mr Thompson and another actor-turned-politician, Ronald Reagan.
The actor has asked to leave Law & Order, where he has played the astute, fatherly New York District Attorney Arthur Branch for the past five seasons, in order to concentrate on politics.
He is also known to viewers for roles in the films The Hunt for Red October, in which he played a US Navy admiral, Last Best Chance and In the Line of Fire.