The president called the killing of bin Laden the "most significant achievement to date" in the effort to defeat al Qaeda.
Bin Laden was located at a compound in Abbottabad, Pakistan, which was monitored and when the time was determined to be right, the president said, he authorized a "targeted operation."
"A small team of Americans carried out the operation," Obama said. "After a firefight, they killed Osama bin Laden and took custody of his body."
DNA testing confirmed that it was bin Laden, sources told ABC News.
Sources said the attack was carried out by Joint Special Operations Command forces working with the CIA.
A Pakistani intelligence official tells ABC News that this was a joint U.S.-Pakistani operation and that last night at 1:30am local time, two American helicopters swooped into Abbottabad, a town about 100 miles from Islamabad.
One of the helicopters was shot down, according to this Pakistani official.
Vice President Biden briefed Republican congressional leaders this evening on the operation, which had been kept secret until shortly before the president's announcement tonight.
Former President George W. Bush said in a statement tonight that Obama called him to inform him of the news of bin Laden's death.
Bush called the operation a "momentous achievement" that "marks a victory for America, for people who seek peace around the world, and for all those who lost loved ones on September 11, 2001.
"I congratulated him and the men and women of our military and intelligence communities who devoted their lives to this mission. They have our everlasting gratitude," the former president said in a statement. "The fight against terror goes on, but tonight America has sent an unmistakable message: No matter how long it takes, justice will be done."
Outside the White House, a crowd of about 200 people has gathered with American flags. They are singing the Star Spangled banner and chanting "USA USA"
His death brings to an end a tumultuous life that saw bin Laden go from being the carefree son of a Saudi billionaire, to terrorist leader and the most wanted man in the world.
Bin Laden created and funded the al Qaeda terror network, which was responsible for the Sept. 11, 2001, attacks on the United States. The Saudi exile had been a man on the run since the U.S.-led invasion of Afghanistan overthrew the ruling Taliban regime, which harbored bin Laden.
In a video filmed two months after the Sept. 11 attacks, bin Laden gloated about the attack, saying it had exceeded even his "optimistic" calculations.
"Our terrorism is against America. Our terrorism is a blessed terrorism to prevent the unjust person from committing injustice and to stop American support for Israel, which kills our sons," he said in the video.
Long before the Sept. 11 attacks, bin Laden was known as an enemy of the United States. He was suspected of playing large roles in the 1998 bombings of two U.S. Embassies in Africa and the attack on the USS Cole in the Yemeni port of Aden in October 2000.
In addition, authorities say bin Laden and his al Qaeda network were involved in previous attacks against U.S. interests -- including the 1993 World Trade Center bombing, failed plots to kill President Clinton and the pope, and attacks on U.S. troops in Saudi Arabia and Somalia.
Bin Laden also used his millions to bankroll terrorist training camps in Sudan, the Philippines and Afghanistan, sending "holy warriors" to foment revolution and fight with fundamentalist Muslim forces across North Africa, in Chechnya, Tajikistan and Bosnia.
Until the capture of one of his top al Qaeda lieutenants in March 2003, there had been no confirmation of his whereabouts -- or even that he was still alive -- since late 2001, when he appeared in a series of videotapes later released to news organizations.
In recent years, several audio recordings of bin Laden have been authenticated by U.S. officials and made public. In an 18-minute videotape weeks before the 2004 U.S. presidential election, bin Laden threatened fresh attacks on the United States as well as his intent to push America into bankruptcy.
Young Man With a Privileged Life
Born in 1957, bin Laden was a son of Saudi Arabia's wealthiest construction magnate. Saudi sources remembered him as a typical young man whose intense religiosity began to emerge as he grew fascinated with the ancient mosques of Mecca and Medina, which his family's company was involved in rebuilding.
Bin Laden attended schools in Jedda, Saudi Arabia, and was encouraged to marry early, at the age of 17, to a Syrian girl and family relation. She was to be the first of several wives. He attended King Abdul-Aziz University and was slated to join the family business. He soon chose a different path, however.
Former classmates of bin Laden recall him as a frequent patron of nightclubs, who drank and caroused with his Saudi royalty cohorts. Yet it was also at the university that bin Laden met the Muslim fundamentalist Sheik Abdullah Azzam, perhaps his first teacher of religious politics and his earliest radical influence.
Azzam spoke fervently of the need to liberate Islamic nations from foreign interests and interventions, and he indoctrinated his disciples in the strictest tenets of the Muslim faith. Bin Laden, however, would eventually cultivate a brand of militant religious extremism that exceeded his teacher's.
He began his relationship with fundamental Islamic groups in the early 1970s. His religious passion exploded in 1979 when Russia invaded Afghanistan. Bin Laden left his comfortable Saudi home for Afghanistan to participate in the Afghan jihad, or holy war, against the Soviet Union -- a cause that the United States funded, pouring $3 billion into the Afghan resistance via the CIA.
Turning Against the Saudi Elite
His active opposition to the Soviet Union and his monetary support in purchasing arms, establishing training camps, and building houses, roads and other infrastructure, cemented his position as a hero among many people.
In 1988, he and the Egyptians founded al Qaeda, ("The Base"), a network initially designed to build fighting power for the Afghan resistance.
Bin Laden's politics became more radical during the war. Upon returning to his home in Saudi Arabia, he was widely honored as a hero. But he returned to a country that he perceived had stepped away from the fundamentals of Islam. He declared the Saudi ruling family "insufficiently Islamic" and increasingly advocated the use of violence to force movement toward extremism.
Bin Laden saw American influence in Saudi Arabia as counter to everything he believed. He fell into disfavor with the Saudi government and moved his family to Sudan where he established terrorist camps -- training and equipping terrorists from a dozen countries.
Bin Laden would not compromise his religious beliefs and after three years of continued criticism of the Saudi royal family, his own family disowned him.
Saudi Arabia stripped bin Laden of his citizenship in the mid-'90s for his alleged activities against the royal family, after he had left the country for Sudan. He later was expelled from Sudan under U.S., Egyptian and Saudi pressure. In 1996, he took refuge in Afghanistan.
Back to Afghanistan
Former mujahideen commanders close to the Taliban said that, in Afghanistan, bin Laden bankrolled the hard-line Islamic militia's capture of Kabul under the leadership of Mullah Mohammed Omar. He became one of Omar's most trusted advisers.
One of bin Laden's main strengths among the Muslim people was that followers saw him as a true believer in the faith. In their eyes he transcended other leaders who are viewed as dictators who care little for Islam or the people they lead. Bin Laden entered their lives with a message they can follow and he had the cash at his disposal to carry out that message.
Bin Laden was said to personally control about $300 million of his family's $5 billion fortune. His role as a financier of terrorism is pivotal, experts said, because he revolutionized the financing of extremist movements by forming and funding his own private terror network.
In 1998, he issued an edict openly declared war on America: "We -- with God's help -- call on every Muslim who believes in God and wishes to be rewarded to comply with God's order to kill the Americans and plunder their money wherever and whenever they find it."
Bin Laden committed himself to expelling all Americans and Jews from Muslim holy lands. "Osama bin Laden may be the most dangerous non-state terrorist in the world," Sandy Berger, President Clinton's national security adviser, told ABC News.
Most Wanted Man on Earth
His place in American history is relatively new, but in a short time he left a violent mark.
In 1993, bin Laden was linked by U.S. officials to the bombing of the World Trade Center that killed six people. He is also believed to have orchestrated at least a dozen attacks, some successful, some not. Among the worst of these were two truck bombings, both on Aug. 7, 1998, of U.S. embassies in Nairobi, Kenya, and Dar es Salaam, Tanzania.
Clinton responded with cruise missile attacks on suspected al Qaeda training camps in Afghanistan and a pharmaceutical plant in Sudan. In November 1998, the U.S. State Department promised $5 million to anyone with information leading to bin Laden's arrest.
Despite attempts to apprehend him, bin Laden eluded the American government and continued plotting against it.
The same group, with bin Laden at the helm, is widely believed to be responsible for the October 2000 suicide bombing of the USS Cole.
Then came the stunning Sept. 11, 2001, attacks. On a clear, late-summer morning, two hijacked commercial jets flew into the twin towers of the World Trade Center. About an hour later, another hijacked airliner slammed into the Pentagon in the nation's capital. A fourth hijacked jet did not reach its target, crashing in western Pennsylvania instead.
When the massive towers collapsed in flames, nearly 3,000 people perished. Among those lost in New York, Washington, D.C., and Pennsylvania were the 19 hijackers, most of whom have been linked to al Qaeda operations. Bin Laden denied involvement in the attacks, but he praised the hijackers for their acts. The U.S. government nevertheless regarded the terrorist leader as its prime suspect and stepped up the manhunt.
In March 2005, Pakistani President Gen. Pervez Musharraf admitted that bin Laden had been in Pakistan in the spring of 2004 and was almost captured. Intelligence officials said they believed he was hiding in the rugged mountains that straddle the border with Afghanistan. The U.S. government even launched a series of television and radio ads in Pakistan trumpeting the $25 million reward for his capture.
In January 2006, a purported Bin Laden audio tape was released where a male voice threatens the United States with more attacks on U.S. soil.