(CNN) -- When Sen. Barack Obama accepts his party's presidential nomination at the Democratic National Convention in Denver, Colorado, he will have experienced one of the most rapid -- and unexpected -- ascents in American political history.

Barack Obama entered politics in 1996, when he was elected unopposed to the Illinois state Senate. more photos »

Obama, an Illinois Democrat, burst onto the national stage in 2004, when he electrified the convention with a keynote address that called for the end of the divisive politics that have pitted Americans against each other.

"There's not a liberal America and a conservative America; there is the United States of America. There's not a black America and a white America and Latino America and Asian America; there is the United States of America," Obama told the delegates.

It was a message Obama may have been uniquely able to deliver, because he has straddled divisions his entire life. Born in Hawaii in 1961, Obama is the son of a black man from Kenya and a white woman from Kansas. When Obama was 2, his father left Hawaii to pursue a degree at Harvard University and later returned to Kenya; Obama saw him only once when he was growing up. See Obama timeline »

"All my life, I had carried a single image of my father, one that I had sometimes rebelled against but had never questioned, one that I had later tried to take as my own. The brilliant scholar, the generous friend, the upstanding leader -- my father had been all those things," Obama said in his 1995 autobiography, "Dreams from My Father." Test your knowledge of Obama »

"All those things and more, because except for that one brief visit in Hawaii, he had never been present to foil the image, because I hadn't seen what perhaps most men see at some point in their lives: their father's body shrinking, their father's best hopes dashed, their father's face lined with grief and regret."

Obama later lived with his mother and stepfather in Indonesia until age 10, when he moved back to Hawaii to live with his maternal grandparents. In his autobiography, Obama describes a troubled adolescence in which he struggled with his biracial identity. He acknowledges that he used marijuana and cocaine.

After high school, Obama attended college in Los Angeles, California, and New York before working as a community organizer on the south side of Chicago, Illinois, from 1985 to 1988.

He attended Harvard Law School, where he became the first black president of the prestigious Harvard Law Review, and returned to Chicago after graduating in 1991 to work as a civil rights lawyer and teach constitutional law. There he met his future wife, Michelle Robinson, a Chicago native. Watch Michelle Obama talk about her husband's style »

Obama's career as a politician began in 1996, when he was elected unopposed to the Illinois state Senate. While in office, he helped pass welfare reform legislation, a state earned-income tax credit, ethics reform and a bill requiring the videotaping of police interrogations and confessions in murder cases.

Obama first took a stab at national politics when he challenged Rep. Bobby Rush, a Chicago Democrat and a former Black Panther, in 2000. Obama lost badly to Rush in the Democratic primary, but, four years later, he made a second attempt to be elected to Congress, running as the Democratic candidate from Illinois for the U.S. Senate. See Obama on the campaign trail »

After his speech at the national convention and scandals involving his Republican challenger, Obama won by a wide margin and arrived in Washington with national prominence, a rarity for a freshman senator. He was often mentioned as a future presidential nominee.

That White House bid came much sooner than many had expected. After just three years in the Senate, Obama formed a presidential exploratory committee in January 2007 and one month later launched his presidential campaign on the steps of the old Statehouse in Springfield, Illinois.

At the time, Obama's chances of winning the Democratic presidential nomination appeared to be a long shot. Hillary Clinton, the senator from New York and former first lady, was viewed as the candidate to beat, and many more experienced contenders -- including fellow senators Joe Biden of Delaware and Christopher Dodd of Connecticut, former Sen. John Edwards and New Mexico Gov. Bill Richardson -- were running to be the "un-Hillary" candidate.

Although Clinton continued to enjoy a large lead throughout 2007, Obama emerged as her main challenger and slowly began to erode her lead in the polls.

Clinton's "inevitable" status cracked when Obama won the Iowa caucuses in January. She came in a surprising third, with 29 percent, just behind Edwards, who had 30 percent.

The New York senator was able to become the latest "comeback kid" in the Clinton family when she won the New Hampshire primary three days later, and the race essentially turned into a two-person contest that latest throughout the spring.

After Obama won the South Carolina primary and the two candidates split the Super Tuesday contests -- Clinton won large states like California and New York, but Obama won more states -- Obama won 13 straight contests in February and built a sizeable lead in pledged delegates.

After Obama's winning streak, some within the party began calling for Clinton to drop out of the race, but she kept her campaign alive by winning in Pennsylvania, Texas and Ohio.

Throughout the primary season, Obama fought constant rumors that were circulated via anonymous e-mail messages and Web sites, including rumors that he was a Muslim (he is a Christian) and that he was educated at a madrassa when he lived in Indonesia.

CNN and other media organizations debunked the madrassa rumor by traveling to Indonesia and finding that the school Obama attended was a secular institution that taught the Koran as part of a basic religious class.

As the protracted primary fight headed into March, Obama's relationship with the Rev. Jeremiah Wright, his onetime pastor at Trinity United Church of Christ in Chicago, came under scrutiny after video of Wright's sermon's circulated on the Internet. In one of the most controversial clips, Wright says blacks should sing "God damn America" rather than "God Bless America" after the attacks of September 11.

Although many viewed the media scrutiny of Wright's sermons as an attack on the black church, Obama repudiated Wright's comments and made a major speech on race. He eventually left Trinity, the church where he was married and where his two daughters were baptized.

In April, before the Pennsylvania primary, comments Obama made at a private fundraiser in San Francisco, California, drew further criticism. He said that many Americans in small towns in Pennsylvania and across the Midwest were "bitter" because of their declining economic situation, which, he suggested, caused them to "cling to guns or religion."

The comments, posted on the Huffington Post Web site, drew charges that Obama was an "elitist" from Clinton and his conservative critics. The criticisms echoed those made when Michelle Obama said during an appearance in Milwaukee, Wisconsin, in February, that "for the first time in my adult lifetime, I am really proud of my country."

Despite Obama's stumbles, Clinton was not able to overcome his lead in the pledged delegate count, although the Democratic contest continued until the final contests in Montana and South Dakota on June 3. That night, Obama, before a raucous crowd in Minneapolis, Minnesota, declared that he would be the Democratic nominee, and in an emotional speech, Clinton conceded the race and threw her support to Obama four days later.

It was an outcome that few would have predicted when the voting began in January, and, as the Democrats gather in Denver, they will be making history by naming Obama the first African-American nominee of a major party.

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