The former general who led Nato forces during the Kosovo campaign has entered the race to win the US presidency in 2004.
Clark has never held elected office
Retired General Wesley Clark, 58, announced his decision to seek the Democratic nomination to run against George W Bush before supporters in his hometown of Little Rock, Arkansas.
Promising " a historic campaign for historic times", Mr Clark said he would focus on national security and the economy.
Analysts say Mr Clark's military background could make him a strong contender but he has no political experience and joins an already crowded field bidding to become the Democrats' candidate.
"My name is Wes Clark, I'm from Little Rock, Arkansas, and I intend to seek the presidency of the United States of America," Mr Clark told the cheering crowd.
He immediately went on the attack, pledging to ask difficult questions of the Bush administration.
"Why has America lost 2.7 million jobs?" he said. "Why has our country lost its sense of security and feels the shadow of fear?"
The former Vietnam veteran said: "For the first time since the 1970s we have more than 100,000 troops fighting abroad and the first time since the Cold War, many Americans no longer feel safe in their homes."
His supporters believe Mr Clark can emulate Dwight Eisenhower, Nato's first supreme commander, who went on to become US President over half a century ago.
They stress that his military career could make him a formidable candidate, capable of undercutting Mr Bush's wartime popularity.
But his critics point out that he has raised little campaign money so far and has no political base in the Democratic Party.
Iraq war opposition
Nine other Democrats are so far seeking their party's nomination, including former governor Howard Dean and Senator John Kerry.
Mr Clark shares Mr Dean's opposition to the US-led war in Iraq and Senator Kerry's distinguished record of service in Vietnam.
Analysts have speculated that the former general's decision to run could lead an even higher-profile candidate to toss her hat into the ring - Senator Hillary Clinton.
She has consistently denied that she plans to seek the White House in 2004 but her denials have failed to quash rumours of her interest.
She might calculate that a successful Clark run in 2004 would make it impossible for her to run in 2008, forcing her to join the fray now.
Scholar and soldier
Like former US President Bill Clinton, Wesley Clark grew up in Arkansas and went on to become a Rhodes scholar at Oxford University, where he took a Master's Degree in Philosophy, Politics and Economics.
But he had already set his heart on a military career. He graduated top of his class at the West Point military academy, and won a Purple Heart in Vietnam after his infantry unit came under fire.
He worked his way up to the top of the chain of command, and led Nato forces in the alliance's first-ever war, in Kosovo in 1999.
Since leaving the military in May 2000, Wesley Clark has set up a strategy consultancy and joined an investment bank based in his home town.
Analysts say he would therefore be in a good position to fight a campaign dominated by the Iraq question - particularly if instability grows there and vindicates his opposition to ousting Saddam Hussein.