Dr Abdullah has played a key role in Afghanistan's foreign affairs
Abdullah Abdullah - an ex-cabinet minister sacked in 2006 - made a remarkable comeback to challenge Hamid Karzai for the presidency.
The Tajik-Pashtun former eye surgeon won 31% of valid votes cast in the August election.
But he decided against standing in the second round, predicting there would be a repeat of the fraud of the first round.
Among the conditions he set was the sacking of the head of the country's Independent Election Commission (IEC), Azizullah Lodin.
Dr Abdullah, 49, became involved in refugee work in Pakistan and later gravitated towards Afghan resistance hero Ahmed Shah Masood, becoming his senior adviser in the 1980s.
Serving as foreign minister in the short-lived government headed by the Northern Alliance, Dr Abdullah continued as "foreign minister in exile" throughout the years of rule by the Taliban, which was ousted in 2001.
There is some confusion over whether his name should have two elements or one, the latter being the style for many Afghan names.
Some reports suggest the second "Abdullah" emerged as a result of a misunderstanding at a news conference.
Fluent in both English and French, he served as spokesman for Gen Masood abroad, emerging as the best-known face of Afghanistan.
Dr Abdullah speaks of "disconnect" between Mr Karzai's and the public
Dr Abdullah continued in that role after Gen Masood's assassination in 2001 under the Karzai government that was formed after the fall of the Taliban.
The cabinet was dominated by the Northern Alliance - something that incumbent President Karzai sought to change.
Karzai supporters see this trend as redressing an imbalance, but critics say he has unfairly marginalised the alliance, which fought the Taliban until the bitter end.
Dr Abdullah lacked his own power base within the Northern Alliance, which might explain why he lasted so long in the Karzai government - but could also be the reason for his eventual replacement as foreign minister.
The suave and smooth-talking former minister said during the 2009 election campaign: "Karzai turned a golden opportunity into disaster. There's no point giving him five more years."
Dr Abdullah has also frequently drawn attention to what he calls the "disconnect" between Mr Karzai's government and a public "alienated by corruption", and a Taliban-led insurgency.
But many argued that he remains tainted by his earlier association with the president.