Before President Barack Obama takes the stage at the Democratic National Convention , U.S. voters will hear from Vice President Joe Biden.

Four years ago, many Democrats saw then-Senator Biden as the voice of experience on a presidential ticket headed by the young Barack Obama. And supporters say the 69-year-old vice president has excelled in the role.

They credit Biden with helping to oversee the end of the war in Iraq and successfully overseeing the billions of dollars in stimulus funds used to try to revive the country's struggling economy.

To the delight of critics, Biden also has lived up to his reputation for delivering poorly-worded quips .

Two years ago, after introducing President Obama following the passage of the controversial health care reform legislation, Biden used a crude expletive that was picked up by a microphone and broadcast to the nation. And just last month, on the campaign trail, Biden told a crowd “they [Republican presidential candidate Mitt Romney and his supporters] are going to put you all back in chains,” referencing slavery. Some African Americans and many others found the comment offensive.

Before becoming vice president, Biden was one of the country's longest-serving senators, working primarily as chairman of the Senate Foreign Relations Committee.

Biden was born in the key battleground state of Pennsylvania and comes from a blue-collar, Roman Catholic family — a fact that may appeal to white working class voters.

Biden also has been a presidential candidate, initially running against Mr. Obama in the 2008 primaries. And during an earlier campaign in 1988, Biden dropped out of the race after being accused of plagiarizing a speech from British Labor Leader Neal Kinnock.

Senator Biden is married and has three living children. His first wife and a daughter were killed in a 1972 car accident, shortly after his first Senate win.