CHICAGO -- The first black to be elected president of the United States ascended the stage at a huge victory rally in downtown Chicago last night and declared that in sweeping aside age-old racial barriers and granting him a victory, America had proved that "a government of the people, by the people and for the people has not perished from this Earth. This is your victory."

"If there is anyone out there who still doubts that America is a place where all things are possible, who still wonders if the dream of our founders is alive in our time, who still questions the power of our democracy, tonight is your answer," President-elect Barack Obama said in a subdued but firmly delivered 15-minute speech to a rapt throng. Spotlights pierced the sky and flashes from thousands of cell phone cameras glittered as rally-goers tried to capture the moment.

That answer, Mr. Obama went on, could be found in the massive voter turnout that marked an extraordinary election day, in "lines that stretched around schools and churches in numbers this nation has never seen, by people who waited three hours and four hours, many for the very first time in their lives, because they believed that this time must be different, that their voice could be that difference."

Joined by his wife, Michelle, whom he called "the love of my life," and two daughters, Malia and Sasha, who he said would get their promised puppy, Mr. Obama spoke against the glittering backdrop of Chicago's skyline and thanked his Republican rival, Arizona Sen. John McCain, to whom he spoke earlier in the evening.

An estimated crowd of 125,000 jammed into the historic park, named in 1901 for Ulysses S. Grant. The scene of numerous 19th century political conventions -- and more recently, numerous rock concerts -- Grant Park holds another infamous distinction: It is the site where antiwar protesters were teargassed while battling police outside the Democratic National Convention in 1968.

Mr. Obama seemed to relish the symbolism of his appearance at the park, invoking Abraham Lincoln and Martin Luther King, noting that his victory marks a new era of reconciliation in a country riven in recent years by political division. Yet his speech contained little in the way of soaring rhetoric. Instead, he sounded a cautionary note about the difficult tasks he and the country face in the months ahead.

"There will be setbacks and false starts," he noted. "There are many who won't agree with every decision or policy I make as President, and we know that government can't solve every problem. But I will always be honest with you about the challenges we face. I will listen to you, especially when we disagree."

The prospect of such dissension didn't seem to faze Joe Parsons, a 35-year old salesman from the West Loop neighborhood of Chicago who had slipped into the press area after facing long lines elsewhere in the park.

He said he was overcome with emotion the moment Mr. Obama's victory was broadcast on the large Jumbotron TVs scattered near the stage.

"I feel privileged, I feel lucky, I feel blessed," Mr. Parsons said. "It's so great to see a man such as Barack Obama, with a goal and dream, to want to make a change, and to see the United States come together to elect him as president. As an African American, it shows we have changed a lot. We have a long way to go, but we've come a long way. Not only does Barack Obama and his wife Michelle deserve credit, but I think America deserves credit, too."

Two women crowded against a chain link fence had waited for hours to get into the ticketed area. Ann Smith, 50, of Chicago, called the unseasonably pleasant weather "divine intervention. Mr. Obama, he's the man, and I love him."

Not long after CNN -- whose election coverage was broadcast on giant Jumbotron monitors scattered around the park -- announced that Ohio had gone for Mr. Obama, Adam Crawford let out a cheer.

"That's money in the bank," said Mr. Crawford, a 35-year-old salesman and Chicago resident. "I didn't come here for nothing."

Gowhara Zimllabedin, who emigrated from Ethiopia years ago, said she'd traveled around the United States as a volunteer for Mr. Obama this year. "I find him so different from anybody else because he will tell the world what he is going to do," said Ms. Zimllabedin, a 45-year-old free-lance photographer. "I think he's a gift. People can learn from him and he is a person who learns from others. I feel that in my heart and soul," she said

Mr. Obama's life story is the most remarkable and improbable of any recent American presidential candidate's -- save, perhaps, for Mr. McCain's.

He is the transformative candidate whose life was a series of self-imposed transformations: son of a white mother from Kansas and a black father from Kenya, he evolved from shy youth and "outsider" to self-confident, Ivy-League-educated adult at ease in any situation; from idealistic, untested community organizer to pragmatic politician; from non-believer to Christian; from rookie state senator whose skeptical colleagues made fun of his exotic name to the newly elected leader of the free world.

Mr. Obama's political rise was fueled as much, if not more, by that unique biography -- skillfully packaged and movingly detailed in two best-selling memoirs -- than by any deep record of legislative accomplishment.

His is a polyglot resume almost perfectly tailored to appeal to a wide range of voters. For the elites, there was the Harvard Law School degree and his place as the first black editor of the school's law review, the most prestigious legal publication in America.

For white, working class America, there was the white grandfather who helped raise him, a man who fought in Patton's Third Army in World War II. For black Americans, there was Mr. Obama's community organizing in Chicago's rougher neighborhoods and -- in case some had doubts that he was "black enough" -- a long struggle with his "outsider" status that ultimately led to his embrace of his black identity.

That journey began in 1961 in Hawaii, where he was born to Ann Dunham, a 19-year-old who had met his father, Barack Obama Sr., in a Russian language class at the University of Hawaii. She was restless, intellectually curious, unconventional. He was a commanding presence, a big talker, charismatic.

The union didn't last. In 1963, Mr. Obama senior left the family to study at Harvard and, from there, returned to Kenya for an up and down career in the newly independent nation. His son never saw him again, except for one month-long visit in Hawaii when the younger Obama was 10.

Ann Dunham married again, this time to an Indonesian, following him to Jakarta in 1966 with her son to pursue her work in anthropology. Despite her dreamy nature, she was hard-headed and goal-oriented.

She poured everything she had into her son, fostering a sense of self-assurance and an ease with different cultures, although she found his lack of ambition occasionally frustrating. Mr. Obama, in his memoirs, recalls balking when she'd wake him at 4 a.m. for correspondence courses in English before school, and her response: "This is no picnic for me either, buster."

When he asked to stay in Hawaii for high school, she agreed, at great emotional cost, her daughter now says. Her son says his greatest regret was that he wasn't with her when she died of ovarian cancer in 1995 at age 53.

"I know that she was the kindest, most generous spirit I have ever known, and that what is best in me I owe to her," he wrote.

In Hawaii, Mr. Obama attended Punahou, a well respected prep school. He was a scholarship kid who had trouble fitting in. Mr. Obama, then known as "Barry," made few friends, he later wrote, but when he discovered basketball, he also began to discover himself.

While many of his fellow students came from affluence, the people he found in pickup games outside of school were black. At home, he'd closet himself in his bedroom to read Malcolm X or James Baldwin, privately engaged, he said, "in a fitful interior struggle. I was trying to raise myself to be a black man in America."

That struggle would intensify at Occidental College in Los Angeles, which he attended for two years before transferring to Columbia University in New York in 1981.

After graduating from Columbia, Mr. Obama spent an unsatisfying year in New York working for a small newsletter-publishing and research firm. He worked briefly as a student organizer at City College before moving to Chicago. There, during three years as a community organizer in the city's poor South Side neighborhoods, he encountered further frustrations but also, he wrote, he realized "the power of the African-American religious tradition to spur social change."

Indeed, after hearing the Rev. Jeremiah Wright speak, he joined the United Church of Christ, and was baptized a Christian in 1988. He also discovered his ability to connect with both poor blacks and the city's black political elite. But the work was hard, the hours were long, the pay minimal and the victories incremental. He sought a different avenue for effecting large-scale social change, and decided to go to law school.

When Mr. Obama was elected in 1990 as the first black president of the Harvard Law Review he did so by appealing to conservatives on the selection panel, an early glimpse of the consensus-building style that would serve him well in his later political career. The previous summer, he'd met his future wife, Michelle Robinson, also a Harvard Law grad, while working at a Chicago law firm. They were married in October 1992, and would have two daughters, Malia, born in 1998, and Sasha, born in 2001.

In 1991, Mr. Obama returned to Chicago, practicing civil rights law at a progressive law firm and lecturing part-time at the University of Chicago's law school, settling with his wife in nearby Hyde Park. He led a successful 1992 voter registration drive, which introduced him to the city's black political leadership. In 1996 -- after methodically eliminating every possible opponent, in an early display of his hardball skills -- he won an Illinois state Senate seat.

The state's capital was known for its corruption, a place where reform-minded neophytes quickly fell under the thumb of a few old-guard leaders. Rather than challenging them, Mr. Obama cultivated them -- despite early hazing from black colleagues who viewed his Harvard pedigree and African parentage with suspicion. He was black, but not stereotypically so. He didn't come up in the civil rights movement, wasn't descended from slaves.

Other than a disastrous run in 2000 for veteran incumbent Bobby Rush's congressional seat -- he lost by 31 percentage points -- his progress upward was smooth, aided by luck and good timing, frequent companions along Mr. Obama's political journey. His defeat also taught him a valuable lesson about his natural constituency -- well-educated white elites throughout the city as well as the leftists of Hyde Park and the urban poor. He moved to the political center and, importantly, began building a coalition of supporters that would help him later when he sought national office.

A Democratic resurgence had been underway in Illinois since 1992, fueled by Republican corruption scandals, and when, in 2002, Republican U.S. Sen. Peter Fitzgerald announced he would not seek reelection, Mr. Obama decided to run for the seat, and won it by a 70 percent vote margin, after other stronger, better-known primary candidates fell by the wayside.

By then, though, he'd become a national sensation after delivering the keynote speech that summer at the Democratic National Convention. As he had so many time before, he saw an opportunity and seized it, delivering a powerfully delivered message of biography and connection, one in which he told his own story as a way of asking if the country's future would be shaped by division or optimism, reminding his audience that there is "not a black America and a white America and a Latino America and an Asian America -- there is a United States of America."

Coming after a lifetime of searching for his own place in that country, a life spent rearranging deficits into assets and a rapid political ascent that masked carefully nurtured ambition and planning, those 17 minutes turned him into the political equivalent of a rock star. The final stage in his journey to the presidency had begun.