The son and grandson of Greek prime ministers, Papandreou was seen by critics as a pale shadow of his dynamic and charismatic father, Andreas Papandreou, who founded the Panhellenic Socialist Movement party, or PASOK, and led it with an iron fist to three election victories from 1981-1993.
Some of his friends joined his detractors in calling him "Giorgakis" _ or little George _ a likable but not widely respected figure who could do few things right. Even his 2006 election as president of the Socialist International, a world group of socialist and social democratic parties, was greeted with remarks about how many of his predecessors had been politicians past their prime.
Now, at 57, Papandreou has come into his own after leading his party to a resounding victory over Prime Minister Costas Karamanlis' conservative New Democracy.
Many consider this more a rejection of a failed government than a personal endorsement of Papandreou, but he won Sunday's vote by an unexpectedly wide margin and a secure parliamentary majority.
The outcome is one few had expected in 2007, when Papandreou fended off a challenge to his leadership following PASOK's second successive defeat at the hands of the conservatives.
As a young deputy in the mid-1980s, he wrote a series of articles laying out his vision of a modernized party and distanced himself from some of his father's policies. But he also laid claim to his family's legacy after he became party leader.
He could count on the unwavering support of a hard core of Andreas Papandreou admirers while competing with his challengers, and he shunted aside people who had made their name under previous socialist administrations and promoted relative unknowns as he sought to put his stamp on the party.
Papandreou was born June 16, 1952, in Saint Paul, Minnesota, where his father was a university professor of economics and had married his American mother, the former Margaret Chant.
He spent his early years in the United States and a large part of his youth abroad, as his father, who had returned to Greece and entered politics in the 1960s, was exiled under the 1967-74 dictatorship. Greek was a second language to Papandreou and he has often been criticized for not being sufficiently Greek.
He obtained bachelor's and master's degrees in sociology from Amherst College in the United States and the London School of Economics, and was first elected to parliament in 1981 at the age of 29.
Panandreou served as deputy culture minister from 1985 to 1987, education minister in 1988-89 and 1994-96, deputy foreign minister in 1993-94, alternate foreign minister from 1996 to 1999 and foreign minister in 1999-2004.
In January 2004, then socialist Prime Minister Costas Simitis, facing certain defeat at the polls, appointed Papandreou his successor as party leader, a decision confirmed in an unprecedented election open to all Greeks, not just party members, where over a million people voted.
But his loss to Karamanlis in the 2004 election and Papandreou's distancing himself from the record of the Simitis government cooled the initial enthusiasm and soured his relations with a segment of the Socialist party.
Challenged by party stalwart Evangelos Venizelos in 2007, Papandreou maintained his party leadership with 55 percent of the vote, but he only established himself firmly as Karamanlis' political fortunes deteriorated rapidly over the past year.
With the magnitude of his victory, Papandreou now has a chance to silence his many doubters _ though he still faces the formidable challenges of deteriorating economy, pervasive corruption, worsening crime and terrorism.