|Biden supported the Iraq invasion but has developed into a critic of its conduct [AFP]
Barack Obama, the Democratic presidential candidate, said that he wanted a running mate who would be prepared to step in as president, could help him govern and would challenge him.
In Joe Biden, a 35-year veteran of the Senate, Obama has chosen a Washington insider with extensive experience and a reputation for speaking his own mind.
The chairman of the Senate Foreign Relations Committee, Biden has met many world leaders and is one of the most influential foreign policy voices in the US Congress.
An internationalist and strong supporter of the United Nations, he has been a leading critic of what he sees as the vague, unilateralist approach of George Bush, the incumbent president.
Recently he travelled to the Georgian capital Tbilisi, at the invitation of Mikheil Saakashvili, the president, and criticised Russia's conduct in the conflict over the breakaway region of South Ossetia.
In 2002 Biden voted to authorise the US-led invasion of Iraq, which Obama opposed from the start, but has become a firm critic of the war.
Last year he pushed through a resolution declaring that Bush's so-called troop surge - which has been hailed as a success - was "not in the national interest". He also won praise for a peace plan which would have divided the country along ethnic lines.
Biden also has a personal interest in the conflict, his son Beau, Delaware's district attorney and a national guard reservist, is due to leave for Iraq at the beginning of October.
"I don't want him going," he told the crowd at a state fair crowd in Iowa. "But I don't want my grandsons or granddaughters going back in 15 years. So how we leave makes a big difference."
Many see Biden as the ideal candidate for the traditional role of the vice-presidential candidate, attacking the other party's man, given his love of joining the debates on America's political talk shows.
But his outspoken style has proved a hindrance on occasions, becoming notorious for his long-winded answers.
However, in a debate last year, he countered a question on whether he had the self-discipline to cut down on his trademark style simply saying: "Yes".
A lifelong politician, 65-year-old Biden outdoes even John McCain, Obama's Republican rival, in terms of Senate experience, having served five years more than the Arizona senator.
|Biden is a prominent foreign policy voice recently travelling to Georgia [AFP]
But there are echoes of Obama's youthful idealism in his past, he was one of the youngest politicians ever elected to the Senate and entered the race for the Democratic nomination in 1988 promising to "rekindle the fire of idealism in our society".
He was reluctantly forced to quit that race three months later after he was caught plagiarising lines from a speech given by Neil Kinnock, the then leader of Britain's opposition Labour party.
His latest bid for the White House was short-lived, pulling out of the race after getting less than one per cent in the first nominating conquest in Iowa.
But it did highlight something which could become an issue on the campaign trail as vice-presidential candidate, his propensity for gaffs.
Biden told the New York Observer newspaper: "I mean, you got the first mainstream African-American who is articulate, and bright and clean and a nice-looking guy."
Some took the remark to remark to be racially offensive, but Obama said he was not offended and the matter was dropped.
He was also forced to defend his remark that "you cannot go to a 7-Eleven or a Dunkin' Donuts unless you have a slight Indian accent".Car accident
Biden has suffered his fair share of difficulties, both personal and political, during his 35 years in the Senate. Just weeks after his election in 1972, his first wife Neilia, and 13-month-old daughter, Naomi, were killed in a car accident. His sons Beau and Hunt were badly hurt.
He was sworn in at the hospital bedside of one of his sons and still refuses to work on December 18, the day of the accident.
He remarried 15 years later, having a daughter with his new wife Jill Tracy Jacobs.
The senator himself had a brush with death in February 1988, when he was hospitalised with two brain aneurysms. It was seven months before he could return to the Senate.
Born in 1942, the Roman Catholic son of a Pennsylvania car salesman, Biden could help Obama connect with blue-collar Democrats who the campaign has so far struggled to attract.
He is seen as more down-to-earth than many Senate colleagues commuting by train from Delaware to Washington every day rather than taking a home in the capital.
Source: Al Jazeera and agencies