Sen. Barack Obama, D-Ill., learned grass-roots political organizing in Chicago, as both a civil rights lawyer and director of the Developing Communities Project, which worked with the poor and families whose breadwinners had lost jobs in the declining steel industry.
He also served as a state senator from 1997 to 2004, where he earned a reputation for bipartisanship.
In his biography, "Obama: From Promise to Power," David Mendell portrays Obama as committed to making a difference, occasionally cocky and thin-skinned in private, and a man in a hurry.
To the man who introduced him to organizing and grass-roots politics in Chicago's tough South Side in the mid-1980s, Obama "was extremely idealistic."
Says veteran Chicago organizer Jerry Kellman: "He identified very much with those who were on the outside of things."
Obama's idealism soon met street reality, and some viewed him as an interloper lacking in the authentic experiences of the poor he represented.
He upset some people in Chicago's black community by challenging or confronting established leaders. That included a 2000 primary challenge of Rep. Bobby Rush, D-Ill., which Obama lost badly.
Kellman said in a Dec. 4 interview that as a community organizer, "Barack was effective, and people who had something to protect in terms of turf, in terms of an established power base, would look for ways to discredit him. And the best way to discredit him was to portray him as an outsider."
But both Kellman and Mendell describe an Obama who eventually became more pragmatic, more accepted and, in 2004, triumphant in one of the most effective first steps on the national stage in American political history.
Obama became a protege and key ally of Illinois Senate President Emil Jones.
In a Nov. 16 interview with Gannett News Service, Jones described the young Obama as a "very effective legislator" who gathered bipartisan support for legislation "by working with legislators and getting to know them and not being dogmatic in debate, even though their views may have been different."
Jones saw similar political instincts when Obama said in a debate in July that he would be willing to meet with the leaders of Iran, North Korea, Syria, Cuba and Venezuela.
Obama's critics, most notably Sen. Hillary Clinton, D-N.Y., called his answer naive.
The implication: that Obama's grandiose "let's talk it out" vision might end up with him caving in to or being used for propaganda purposes by enemies of the United States.
"I am not afraid of losing a propaganda battle with some petty dictator," Obama told a University of Virginia audience in October.
Obama - who's been in the Senate less than three years - faces Clinton and a field of Democrats who have much longer resumes on everything from health care policy to the Middle East.
His relative freshness helps him drive home that he is the true change candidate in 2008.
The nation was introduced to Obama when he gave a dynamic, 17-minute speech at the Democratic National Convention in Boston in 2004.
He focused on his story - an update of Horatio Alger - recounting the different worlds of his white mother from Kansas and his black father from Kenya.
His father, Obama said, had grown up herding goats and going to school in a tin-roof shack.
That speech foreshadowed some of the style and substance voters would be seeing more of: his message of inclusiveness and his self-effacing humor, referring to himself as the "skinny kid with a funny name."
Obama often says his wife, Michelle, a Chicago native and, like him, a graduate of Harvard Law School, keeps him humble, and in check.
Obama's campaign rallies are designed to pump up a rock-star persona.
Along the way, Obama has picked up many celebrity backers, none more powerful than media mogul Oprah Winfrey.
Her recent rallies for Obama in South Carolina, Iowa and New Hampshire drew thousands of people.
In debates, however, he is not as smooth, and it is in these free-for-alls that his lack of experience shows.
Obama's overall theme is inclusiveness, change, and what he calls "the audacity of hope."
On race, Obama has a vision designed to inspire fellow blacks on traditional civil rights fronts and honor civil rights pioneers whose sacrifices opened doors for him. He has given strong speeches about being black in America, telling biographer David Mendell, "When I see young African-American men out there and the struggles they go through, I connect with that."
Some have questioned whether Obama's upbringing - which included living with a mother who sometimes struggled economically, living overseas and going to an exclusive Hawaii boarding school - made him "black enough" to understand the problems facing average blacks.
Emil Jones, the Illinois Senate president, discounts that argument and says it is irrelevant for a man who wants to be president of all Americans. "When you run for president of the country, you are not running for the presidency of the black community," Jones says.
Ron Walters, a political scientist at the University of Maryland, says Obama has gone a step further than just offering himself as a president who aspires to bring people together. He says Obama has addressed poverty and offered "clearly articulated" positions on national health care and on the Iraq war.
Obama, 46, is an avowed collaborator. Aides often try to portray him as the opposite of President Bush, who has famously described himself as "the decider" in an attempt to show resolve, consistency and toughness.
"The Bush administration is an insular circle of like-minded people that nod their head every time the boss says something," says Robert Gibbs, Obama's communications director. "The White House needs somebody who is not going to sit around the table agreeing with everything he says."
Gibbs, who has been with Obama since he ran for the Senate in 2004, describes him as "somebody with a tremendous amount of intellectual curiosity who will talk to people who know more about things than he does. He is somebody who makes up his own mind, but he is not going to go out and say he is 'the decider,' meaning he doesn't listen to the viewpoints of anybody else."
The downside of Obama's reflective, collaborative style is that it can make a leader look indecisive.
One example occurred in early November. Several Obama campaign aides anonymously criticized the candidate's reluctance to get tougher with Sen. Hillary Clinton in simultaneous stories in the New York Times and the Washington Post.
The result: Not only did it telegraph what Obama would do in an impending debate, it opened the window to internal dissent and showed that Obama's inner circle was willing to go outside to force changes.
As an example of his willingness to stand alone with resolve, Obama cites his decision to speak out against going to war in Iraq just days before Congress voted to give President Bush the authority to do so. Obama says he spoke out even though friends warned him he might be hurting his political career.
More than anything, Obama has been on the defensive about a lack of management experience. Four of the past five presidents were previously governors.
Obama likes to point out that he has had two decades of experience: as a community organizer, civil rights lawyer, law professor, Illinois state legislator and now as a U.S. senator.
In the debate in Philadelphia, he added: "I think the next president has to be able to get people to work together to get things done, even when they disagree. And I've done that."
Biographer David Mendell writes of several instances in which Obama played middle-of-the-road negotiator in contentious situations, from his time at Harvard Law School, where Obama was the first black president of the Harvard Law Review, through eight years in the Illinois Senate.
At Harvard in the late 1980s and early 1990s, in the midst of a debate over whether the term "black" or "African American" was appropriate, Mendell writes that Obama told fellow law students that the argument was irrelevant. Obama said, "How we use our education in these next three years" to improve the lives of blacks was more important.
After being elected to the Illinois Senate in 1996, representing Chicago's South Side, Obama gained a reputation among Republicans as a Democrat they could work with. His first bill, a campaign finance reform measure, passed 52-4.
Obama also got Republican support for legislation that clamped down on racial profiling by police and for a children's health care measure.
Obama's advisers include several policy wonks from President Clinton's administration.