He called on Americans to leave behind party polarization, saying, "There is not a liberal America and a conservative America; there's the United States of America."
The speech instantly made Obama a star, with political pundits suddenly predicting the state senator who had not yet been elected to the U.S. Senate might someday be positioned for a presidential run.
Rep. Jan Schakowsky, D-Ill., said at the time that during a meeting with President Bush in February of 2004, the Congresswoman wore an Obama button on her coat.
"I don't know him," Bush said, according to Schakowsky.
"Oh, you will, Mr. President," she responded.
Obama's newfound stardom and oratory skills made him a draw at political events and fundraisers across the country, able to attract media attention and raise money for other Democrats.
Expanding on his speech, Obama's 2006 book, "The Audacity of Hope:Thoughts on Reclaiming the American Dream," rocketed up The New York Times best-seller list.
Even his candid admission that he used cocaine and smoked pot in high school and college , in his first book, "Dreams From My Father: A Story of Race and Inheritance," did little to tarnish his image as an up-and-coming political phenomenon.
Announcing his presidential bid in February 2007 on the steps of the Illinois state legislature where Abraham Lincoln gave a famous speech condemning slavery and calling for the United States to unite, Obama said that as president he would heal a divided nation.
"I know that I haven't spent a lot of time learning the ways of Washington. But I've been there long enough to know that the ways of Washington must change," Obama said.
Obama has focused his campaign on pulling U.S. troops out of Iraq, universal health care, and stimulating the economy with a middle-class tax cut.
At a time when the majority of Americans believe the Iraq War was a mistake, Obama reminded voters that his closest Democratic rivals, Clinton and former Sen. John Edwards of North Carolina, voted to give President Bush the authority to wage the war.
Last year, Clinton was considered the front-runner, with big-money donors backing her bid, not to mention a political team mirroring her husband's inner circle and an organized effort to attract women voters.
But Clinton's message of experience, Washington resume and her front-runner strategy left some Democrats cold and open to Obama's and Edwards' anti-Washington message.
Waging an outsider campaign, Obama's campaign raised a record-breaking $58 million during the first half of 2007, and boasted record-breaking support among people donating $200 and less.
Obama also attracted high-profile celebrity endorsements from talk-show queen Oprah Winfrey, and won highly sought-after Democratic establishment support from Sen. Ted Kennedy, D-Mass., Caroline Kennedy, the daughter of former President John F. Kennedy, Sen. John Kerry. D-Mass., and California first lady Maria Shriver.
As voters went to the polls in the early voting states of Iowa, New Hampshire, Nevada and South Carolina, Obama's campaign raised $36.8 million, the most ever raised in one month by a presidential candidate in the Democratic primaries.
Gaining momentum, Obama racked up more convention delegates than Clinton in all of the early contests.