Barack Obama's future vice president, who has three decades' experience in the US Senate and chairs its Foreign Relations Committee, is full of ideas, energy and enthusiasm but his endless chatter and rather careless nature led him to make a series of mistakes.
And, acutely aware of the problems, the Obama campaign effectively muzzled the 65-year-old Delaware senator. He did not give a news conference or interview after September, making him even less accessible than John McCain's running mate Sarah Palin.
And perhaps with good reason - critics attacked Mr Obama as someone who would invite a dangerous confrontation after Mr Biden said the world would "test" the Democrat with a "generated" international crisis within six months.
Mr Biden has also been at odds with Mr Obama on a number of occasions, calling one of his campaign adverts "terrible" and disagreeing with him over some aspects of the US government's handling of the financial crisis.
Mr Obama said his vice president "should have waited" before voicing opposition to the government bailout of US insurance giant AIG last month.
And Mr Biden told CBS News that Democrat Franklin D Roosevelt went on television to reassure America after the 1929 stock market crash - although Republican Herbert Hoover was president during the crash, which predated television.
It came after Mr Biden labelled an Obama campaign advert which depicted Mr McCain as old and out-of-touch, unable to use computers or email, as "terrible".
The Republicans wasted no time seizing on the opportunity, running a Biden "gaffe clock" on their national committee website, counting the "time since Biden's last gaffe".
Even his speech after he was introduced as Mr Obama's running mate was not error free, with Mr Biden calling Mr Obama "Barack America".
Mr McCain's campaign also labelled Mr Biden Mr Obama's harshest critic.
Earlier this year, when he was still in the race for the Democratic Party's nomination, Mr Biden said the Illinois senator was not yet ready to be president and that "the presidency is not something that lends itself to on-the-job training".
In the Senate, he is respected as a thoughtful leader with a passion and commitment to solve America's problems.
Hillary Clinton, who some thought would have created a "dream ticket" as Mr Obama's running mate, said Mr Biden was "an exceptionally strong, experienced leader and devoted public servant" who would be "a purposeful and dynamic vice president".
He strengthened Mr Obama's foreign policy credentials and enabled the president-elect to challenge frequent criticism that he lacked experience in that area.
Talking to voters, Mr Biden said America needed "more than a good soldier" as its next president and former Vietnam prisoner of war Mr McCain only offers "more of the same" of President George Bush's failed policies.
But all too often in front of reporters and TV cameras his talkative and headstrong nature lead to awkward statements, gaffes and goofy smiles.
On 31 January last year, the same day he announced his decision to run for the presidency, he said that in Mr Obama, America had "the first mainstream African American who is articulate and bright and clean and a nice-looking guy" - a quote which supplanted any good press he may have earned through his otherwise impressive political stature.
And his first bid for the presidency in 1988 ended amid accusations that he plagiarised an earlier speech by Labour leader Neil Kinnock without acknowledgement.
Whole sentences from Mr Kinnock's speech, as well as glaring similarities in syntax and ideas, seeped into Mr Biden's stump speech and his campaign ground to a halt.
It also emerged that he had used an unattributed quote from Robert Kennedy, president John F Kennedy's brother, and there was another accusation of plagiarism while he was in law school.
Other mistakes include saying that: "You cannot go to a 7-Eleven or a Dunkin' Donuts unless you have a slight Indian accent."
Profiles frequently note his big mouth and capacity to babble, with a New York Times story in July 2007 headlined "In Iowa Yard, Biden Talks (and Talks) about Experience" and a GQ profile in March 2006 which said: "Joe Biden Can't Shut Up".
Born in a working class family in Scranton, Pennsylvania, on 20 November, 1942, Joseph Robinette Biden Jr is of Irish Catholic heritage but is in favour of abortion rights, a key issue in American elections.
He is one of the poorest US senators and his family have kept a relatively low profile to-date, helped by the fact he continues to commute 90 minutes each day from his home in the Wilmington suburbs to Washington, DC.
Mr Biden is not a household name, but was arguably the most well-known of those considered by Mr Obama, and first ran for the US Senate when he was 29 years old.
He originally voted to authorise the war in Iraq, but has since become a persistent critic of the Bush administration's policies there.
He was also the chairman of the Senate Judiciary Committee during two of the most contentious Supreme Court nomination battles of the past 50 years.
He led the opposition to the nominations of Robert H Bork, who was defeated, and Clarence Thomas, who was later confirmed.
Mr Biden married Neilia Hunter in 1966 and the couple had three children.
But his wife and 13-month-old daughter Naomi died in a car accident on 18 December 1972, shortly after he was first elected to the US Senate.
His two sons, Joseph R "Beau" Biden III and Robert Hunter, were seriously injured, but Mr Biden was persuaded not to resign to look after them and was sworn into office from their bedside.
Both have since made full recoveries.
In 1977 he married Jill Tracy Jacobs, with whom he has one daughter, Ashley.
They have been together since, but his wife has retained a low profile.
As he brought her into a world of much closer scrutiny, his unclear comments showed no indication he had put his gaffes behind him.
"Ladies and gentlemen, my wife Jill, who you'll meet soon, is drop dead gorgeous. My wife Jill, who you'll meet soon, she also has her doctorate degree, which is a problem."
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