Mousavi has been involved in Iranian politics since the start of the revolution
Mir Hossein Mousavi - the main challenger to conservative Iranian President Mahmoud Ahmadinejad - has not always moved in liberal circles.
And neither is the president of the Iranian Academy of Arts best known for his love of painting or poetry.
Mr Mousavi was prime minister of Iran for eight years until the post was abolished in 1989.
A 20-year-long hiatus ensued before the 68-year-old man returned to stand as a moderate in the 2009 election.
To describe him as a liberal to Mr Ahmadinejad's hard-line stance would, however, be inaccurate. In 1988, the Economist called him a "firm radical".
Mr Mousavi was born in the East Azerbaijan Province of Iran and moved to Tehran to study architecture at university - he specialises in Islamic architecture.
Mr Mousavi has said his wife is one of Iran's most enlightened women
He and his wife, Zahra Rahnavard, were active in the Islamic revolution that overthrew the Shah.
Mr Mousavi defended the taking and holding of American hostages by Iranian militants in 1979 as serving the revolution's purpose.
In an interview with the New York Times in 1981 he said "it was after this that we rediscovered our true Islamic identity".
As prime minister, Mr Mousavi had the backing of Ayatollah Khomeini, the leader of the revolution, and is remembered as leading a government that did not stand for dissent.
He was also seen as having steered a good course for the economy during the Iran-Iraq war.
When the war ended in August 1988, Mr Mousavi argued heatedly with Ayatollah Ali Akbar Hashemi Rafsanjani, the speaker of Iran's parliament at the time, over his suggestion that Iran should accept the offer of Western help with reconstruction.
Ali Akbar Hashemi Rafsanjani originally did not get on with Mr Mousavi
When Mr Rafsanjani became president in 1989, he refused to invite Mr Mousavi and other hard-liners to join his new government.
It was the start of 20 years of an almost total absence from public life for Mr Mousavi, though he did sit on two high-level regime councils.
Instead he focussed on his architecture and teaching while developing his passion for painting and writing poetry.
Out of the limelight
By 1997, Mr Mousavi had become part of the reformist movement and was seen as its best chance to become president.
However, he refused to stand, clearing the path for Mohammad Khatami to be elected by a landslide.
Both Mr Mousavi and his wife later served as advisers to President Khatami during his eight years as president.
The former president withdrew his candidature in March to endorse Mr Mousavi's campaign.
The reformer also secured the backing of his old rival Rafsanjani, who now heads two of the regime's most powerful bodies: the Expediency Council (which adjudicates disputes over legislation) and the Assembly of Experts (which appoints, and can theoretically replace, the Supreme Leader).
Zahra Rahnavard and Khatami were influential in the campaign
Mr Mousavi said his return to politics was based principally on a belief that Iran was in grave danger, made even more real by the possibility of a second Ahmadinejad term.
He also vowed to combat Iran's "extremist" image abroad.
During his campaign, he called for greater personal freedoms in Iran and criticised the ban on private television channels.
He opposed the West's calls to suspend the country's nuclear-enrichment programme - whilst making a distinction between nuclear power and weaponry.
He told the Financial Times that "the recent discourse, which differentiates between nuclear technology and nuclear weapons is a good one. The more this differentiation is emphasised, the greater the possibility of detente".
Power behind the throne
One of Mr Mousavi's greatest assets during the campaign was his wife, Zahra Rahnavard, one of Iran's most influential women.
She broke with Iranian political tradition by appearing alongside her husband and campaign posters even showed the couple holding hands.
Ms Rahnavard was an active campaigner, making speeches, attending rallies alone and publicly criticising the incumbent President Ahmadinejad for his treatment of women.
A respected scholar and artist in her own right, Ms Rahnavard has described herself and her husband as "unusual".