Four years ago, President Barack Obama 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 chosing then Delaware senator Joe Biden, Obama placed veteran debater who was in the US senate for more than a quarter century and is perhaps the Democratic White House's most passionate defender of the working class on his ticket.
Having previously served as the chariman of the Senate Foreign Relations Committee, the vice-president is one of the most influential foreign policy voices in the US.
The 69-year-old has been credited with being a key player in some of the biggest decisions taken under the Obama administration, including the move to withdraw 30,000 troops from Afghanistan by summer 2012.
Although criticised for not requesting a dedicated portfolio of issues from Obama in 2009 - which Al Gore had gone when he was vice-president under Bill Clinton - he has become the president's point-person on issues ranging from Iraq to budget negotiations in Congress, and oversaw the distribution of the $787bn allocated for spending by the economic stimulus bill.
With a debate scheduled for October 11 against Republican vice-presidential nominee Paul Ryan, Biden is under pressure to help President Barack Obama's campaign recapture the momentum it enjoyed before Obama gave a lacklustre performance first of his three debates with Republican contender Mitt Romney.
Biden 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 last bid for the White House in 2008 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 has been seen as an issue in 2008 and the current re-election campaign: his propensity for gaffes, including his recent remark that the middle class has been "buried for the last four years" - the span of Obama's presidency - by a bad economy.
Biden was referring to the fallout from the recession that began under Republican President George W Bush, but Romney and Ryan pounced on Biden's comment, saying that even Obama's running mate was acknowledging that the president had fallen short in overseeing the economy.
Last spring, Biden also slipped up when he endorsed same-sex marriage on a television interview, a stance that went beyond Obama's statements on the political hot-button issue and put renewed pressure on the president to clarify his views on the topic.
While opponents portray the vice-president as a political buffoon, his defenders say the mistakes are evidence of a straight-talking style that makes him a hit with many voters.
According to Obama campaign manager Jim Messina, Biden has "an ability to connect and communicate in a clear and effective way. He, like the president, embodies an American success story".
His 2012 speech at the Democratic National Convention on September 6 was hailed by Democrats as a clear demonstration of his ability to hit hard with the party's rank and file.
In his speech, he swung hard at Romney and rejected the notion that government-funded college loans and job training create dependency
"Americans have never looked at it that way. These men and women aren't looking for a handout," he said, "They're just looking for a chance to acquire the tools and the skills to provide for their families - so they can hold their heads high and lead independent lives with dignity."
Over the past year alone, Biden has attended well over a hundred political events to promote the re-election campaign, including speeches, fundraisers, and rallies.
Biden has suffered his fair share of difficulties, both personal and political, during his career.
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 is still seen as a link between Obama and blue-collar Democrats.
During his years in the senate, he was considered very "down-to-earth", commuting by train from Delaware to Washington every day rather than taking a home in the capital.