Tariq Aziz, seen as the face of Saddam Hussein's regime for many years, has died in an Iraqi prison.
Mr Aziz (79) served as foreign 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.
Mr Aziz, who was known for his black-rimmed glasses, first came to prominence while serving as foreign minister during the first Gulf War in 1991.
He had long complained of ill health during his detention.
Dr Saadi al-Majid, head of the health department of Dhi Qar governorate, where Mr Aziz was being held, confirmed Mr Aziz's death.
"Tariq Aziz arrived at al-Nasiriya Educational hospital suffering from a severe heart attack. He had heart complications that led to his death at 3 pm."
The governor of Dhi Qar, Yahya al-Nasiri, said the body would be handed over to Mr Aziz's relatives in Iraq "as soon as our routine procedures and investigations are concluded".
Mr Aziz's son Zaid told Reuters in Amman that his mother had visited his father in prison on Thursday and had asked the prison authorities to take him to hospital.
He said the prison had refused, though this could not be confirmed independently.
"His voice was deteriorating but he was not dying," Zaid said.
Mr Aziz, a fluent English speaker, played a prominent diplomatic role in the run-up to the 1991 Gulf War, when a US-led coalition drove Iraqi forces out of Kuwait, as well as in the long-running disputes over United Nations weapons inspections in subsequent years.
A Chaldean Christian, he was born in the village of Tal Keif, near Mosul in northern Iraq.
His association with Saddam dated back to the 1950s, when the two men were involved in the then-outlawed Baath party, which sought to oust the British-backed monarchy.
Mr Aziz was appointed minister of information in the 1970s.
In 1977, he joined the Revolutionary Command Council, the committee of senior Baath party officials ruling Iraq, and in 1979, he became deputy prime minister.
He was number 43 on the US list of most wanted Iraqi officials when he gave himself up just two weeks after Saddam was toppled.