Biden, 65, has twice sought the White House, and is a Catholic with blue-collar roots, a generally liberal voting record and a reputation as a long-winded orator.
Across more than 30 years in the Senate, he has served at various times not only as chairman of the Foreign Relations Committee but also as head of the Judiciary Committee, with its jurisdiction over anti-crime legislation, Supreme Court nominees and Constitutional issues.
In selecting Biden, Obama passed over several other potential running mates, none more prominent than former first lady Hillary Rodham Clinton, his tenacious rival in dozens of primaries and caucuses.
Obama's campaign arranged a debut for the newly minted ticket on Saturday outside the Old State Capitol in Springfield, Ill.
Obama's decision leaked to the media several hours before his aides planned to send a text message announcing the running mate, negating a promise that people who turned over their phone numbers would be the first to know who Obama had chosen. The campaign scrambled to send the text message after the leak, sending phones buzzing at the inconvenient time of just after 3 a.m. on the East Coast.
Hundreds of miles to the west, carpenters, electricians, sound stage gurus and others transformed the Pepsi Center in Denver into a made-for-television convention venue.
Tucked away in one corner were thousands of lightweight rolled cardboard tubes, ready-made handles for signs bearing the names of the Democratic ticket
- once the identity of Obama's running mate was known.
While Obama decided against adding Clinton to his ticket, he has gone to great lengths to gain the confidence of her primary voters, agreeing to allow her name to be placed in nomination at the convention and permitting a roll call vote that threatens to expose lingering divisions within the party.
Biden slowly emerged as Obama's choice across a long day and night of political suspense as other contenders gradually fell away.
First Virginia Gov. Tim Kaine let it be known that he had been ruled out. Then came word that Sen. Evan Bayh of Indiana had also been passed over.
Several aides to Clinton said the Obama campaign had never requested financial or other records from her.
Other finalists in the veep sweepstakes were Kansas Gov. Kathleen Sebelius and Texas Rep. Chet Edwards.
Among those on the short list, Biden brought the most experience in defense or foreign policy
- areas in which Obama fares relatively poorly in the polls compared with Republican Sen. John McCain.
While the war in Iraq has been supplanted as the campaign's top issues by the economy in recent months, the recent Russian invasion of Georgia has returned foreign policy to the forefront.
In addition to foreign policy experience, Biden, a native of Scranton, Pa., has working-class roots that could benefit Obama, who lost the blue-collar vote to Clinton during their competition for the presidential nomination.
Biden was elected to the Senate at the age of 29 in 1972, but personal tragedy struck before he could take office. His wife and their 13-month-old daughter, Naomi, were killed when a tractor-trailer broad-sided her station wagon.
Biden took his oath of office for his first term at the hospital bedside of one of his sons.
On Friday, he spent the day at his home in Delaware with friends and family. The normally loquacious lawmaker maintained a low profile as associates said they believed
- but did not know - he would be tapped. They added they had been asked to stand by in case their help was needed.
No sooner had word spread of his selection than McCain's campaign unleashed its first attack. Spokesman Ben Porritt said in a statement that Biden had "denounced Barack Obama's poor foreign policy judgment and has strongly argued in his own words what Americans are quickly realizing
- that Barack Obama is not ready to be president."
