Tariq Aziz, known as the face of Saddam Hussein's regime on the world stage for many years, has died in an Iraqi hospital, officials say.
Aziz, 79, served as foreign minister and deputy prime minister and was a close adviser to the former leader.
He was sentenced to death by the Iraqi Supreme Court in 2010 for the persecution of religious parties under Saddam's rule but was never executed.
He surrendered to US troops in 2003 shortly after the fall of Baghdad.
A local health official told reporters that he was taken to hospital from prison after suffering a heart attack. Initial reports said he had died in prison.
He had long been in poor health, suffering from heart and respiratory problems, high blood pressure and diabetes, and his family repeatedly called for his release from custody.
His wife, Violet, had visited him in prison on Thursday, their daughter Zeinab told the AP news agency.
She said her father had suffered several strokes that left him confined to a wheelchair and unable to speak during her parents' final meeting.
"He didn't move. He couldn't talk. He didn't say a word to her. He just looked at her," said Zeinab, adding: "It is so sad that he had to go this way."
'Eight of spades'
Aziz, who was known for his black-rimmed glasses and love of cigars, first came to prominence while serving as foreign minister during the first Gulf War in 1991.
As a Christian in a mainly Sunni Muslim government, he was not considered a member of Saddam Hussein's innermost circle.
A fluent English speaker, he played a vocal role before the US invasion of Iraq in 2003, meeting Pope John Paul II in the Vatican to call for peace.
But when Baghdad fell, his lack of influence was reflected in his lowly ranking as the eight of spades in the US military's famous "deck of cards" used to identify the most-wanted players in Saddam's regime.
Analysis: Paul Adams, BBC diplomatic correspondent
Tariq Aziz was one of the most visible of Saddam Hussein's lieutenants and, it seems, one of the most loyal.
He frequently represented Iraq on the international stage, speaking fluent English and giving a monstrous regime an urbane, often charming face. And like Saddam, he was often seen puffing on fat Cuban cigars.
When Iraq found itself in dock, as it did after its invasion of Kuwait in 1990, it invariably fell to Tariq Aziz to explain Saddam's actions to an exasperated world. He did it doggedly, often infuriatingly, for decades.
As an ethnic Chaldean from northern Iraq, he was also the only Christian member of Saddam's entourage, which made him useful as an envoy for an secular regime. It also made him an outsider in Baghdad.
Western diplomats never doubted his loyalty to Saddam, but wondered how much he really knew about his master's secrets.
In 2009, Aziz was sentenced to 15 years for the execution of 42 Iraqi traders who had been accused of manipulating food prices while Iraq was subject to international trade sanctions.
Five months later, he was sentenced to another seven years in prison for his role in the forced displacement of Kurds.
Despite being sentenced to death in 2010, there never seemed any huge pressure to carry out the sentence, according to BBC Arab affairs editor Sebastian Usher.