Amin, who had lived for years in exile in this Saudi port city, died at 8:20 a.m at King Faisal Specialist hospital, a hospital official said on condition of anonymity.
Amin had been hospitalized on life-support since July 18. He was in a coma and suffering from high blood pressure when he was admitted to the hospital. Later, hospital staff, said he suffered kidney failure.
A one-time heavyweight boxing champ and soldier in the British colonial army, Amin seized power on Jan. 25, 1971, overthrowing President Milton Obote while he was abroad.
What followed was a reign of terror laced with buffoonery and a flirtation with Palestinian terrorism that led to the daring 1976 Israeli raid to rescue hijack hostages in his country.
In Kampala, Uganda, President Yoweri Museveni's spokesman called Amin's death "good."
"His death and burial will signal the end of our bad past," the spokesman, Oonapito Ekonioloit, said.
Ugandan officials said Amin was 80, though other sources had him born in 1925.
Obote once called Amin "the greatest brute an African mother has ever brought to life." President Jimmy Carter said events in Uganda during Amin's rule "disgusted the entire civilized world."
Ugandans initially welcomed Amin's rise to power, and his frequent taunting of Britain, former colonial ruler of much of Africa, often played well on the continent.
But his penchant for the cruel and extravagant became evident in 1972, when he expelled tens of thousands of Asians who had controlled the country's economy. Deprived of its business class, the East African nation plummeted into economic chaos.
Michael Mademaga, 41, an office messenger in the Ugandan capital claimed that Amin's agents killed his uncle in 1974.
"I feel happy that he has died. His body should be brought back to Uganda and put on display and people view it and see somebody who killed so many people," Mademaga said.
Amin declared himself president-for-life of his landlocked country of 24 million, awarded himself an array of medals and ran the country with an iron fist, killing real and imagined enemies.
Human rights groups say from 100,000 to 500,000 people were killed during his 8-year rule. Bodies were dumped into the Nile River because graves couldn't be dug fast enough. At one point, so many bodies were fed to crocodiles that the remains occasionally clogged intake ducts at Uganda's main hydroelectric plant at Jinja.
Amin was born into the small Kakwa tribe in Koboko, a village in northwestern Uganda. His mother was a self-proclaimed sorceress of the Lugbara tribe and he was in his 30's before he had regular contact with his peasant father.
A semiliterate school dropout, Amin boasted that he knew "more than doctors of philosophy because as a military man I know how to act."
"I am a man of action," he said.
And words. He said Hitler "was right to burn six million Jews," and offered to be king of Scotland if asked. He challenged his neighbor and frequent critic, Tanzanian President Julius Nyerere, to a boxing match, and wrote to Richard Nixon wishing him "a speedy recovery" from Watergate.
Amin was a well-regarded officer at the time of Uganda's independence from Britain in 1962, and Obote made him military chief of staff in 1966.
The 250-pound president called himself Dada, or "Big Daddy," and in 1975 was even chosen as for the one-year rotating chairmanship of the Organization of African Unity despite objections from some member states.
But mismanagement and corruption of his entourage drove Uganda into an abyss and its economy tumbled toward subsistence levels. The United States and Britain severed ties during Amin's rule. Israel went from staunch military and economic ally to hated enemy for refusing to support his aggressive military ambitions.
In 1976 a Palestinian group hijacked an Air France airliner to Entebbe Airport in Uganda and kept its Israeli passengers as hostages. Israeli commandos flew to Entebbe under cover of darkness and rescued the captives. Amin claimed he had been trying to negotiate a peaceful resolution, but there was plenty of evidence that he was in league with the hijackers.
Amin's overreaching designs led to his downfall after his troops failed in their attempt to annex parts of Tanzania in Oct. 1978. Tanzanian troops counter-invaded, routed Amin's Soviet- and Arab-equipped army and reached the Ugandan capital, Kampala, in April 1979.
Amin, a convert to Islam, fled to Libya, then Iraq and finally Saudi Arabia, where he was allowed to settle provided he stayed out of politics. In later months, he was joined by one of his two wives and his 22 children.
Obote returned to power in 1980 elections and unleashed what many felt was an even worse repression than Amin's. Since 1986 Uganda has been ruled by Museveni. Uganda remains a one-party state but has gradually returned to relative peace and normality.
Amin, meanwhile, moved into a luxury house in the Red Sea port city of Jiddah, with cars, drivers, cooks and maids paid for by the Saudi government. He would occasionally telephone journalists abroad to announce fantastical schemes to reconquer Uganda, or to protest against cuts in his gasoline allowance. But the Saudis got angry and made him stop.
In a rare interview in 1999, Amin told a Ugandan newspaper he liked to play the accordion, fish, swim, recite from the Quran and read. He said most of his food — including fresh cassava, cassava flour and millet flour — still came from Uganda.
He was sometimes spotted on evening walks along the coast or attending Friday prayers in a nearby mosque.
Amin is believed to have married at least four times and had some 30 children, many of whom had joined him in exile in Saudi Arabia.
In Kampala, one of his sons, Ali Amin Ramadhan, 40, said he did not know yet where his father would be buried. "I am very sad and confused," he said.