Former Chad leader Hissene Habre is "Africa's Pinochet", according to pressure group Human Rights Watch (HRW).
A Commission of Inquiry formed after he was deposed in 1990 said his government carried out some 40,000 politically motivated murders and 200,000 cases of torture in the eight years he was in power.
Chadians have been trying to bring Mr Habre to justice for 15 years
His dreaded political police force, the Documentation and Security Directorate (DDS), is accused of some of the worst abuses.
Mr Habre, 64, denies any knowledge of murders and torture.
He seized power in 1982 from Goukouni Oueddei, a former rebel comrade who had won elections.
It was widely believed that he was backed by the CIA, as a bulwark against Libya's Colonel Muammar Gaddafi.
His coup came in the middle of a war with Libya over the disputed Aozou strip.
Backed by the United States and France, Mr Habre's forces drove out the Libyans in 1983.
He first came to the world's attention in 1974 when a group of his rebels captured three European hostages and demanded a ransom of 10 million francs.
One of the hostages, French ethnologist Francoise Claustre, was held for 33 months in the caves of Tibesti volcanic complex of northern Chad.
However, this episode did not prevent the French from later backing Mr Habre.
He was born to ethnic Toubou herders in northern Chad but excelled at school and was eventually spotted by a French military commander, who organised a grant for him to study in France.
As a senior local official, he was sent to persuade two rebel chiefs, including Mr Oueddei, to lay down their arms; instead he joined their struggle.
During Mr Habre's time in power, he faced a succession of rebellions but lobby group Amnesty International says this does not excuse his government's human rights abuses.
"The Chadian government applied a deliberate policy of terror in order to discourage opposition of any kind," Amnesty says.
Human rights groups say the DDS was under the tight personal control of Mr Habre.
An underground prison, known as the "Piscine" because it was a converted swimming pool was one of the DDS's most notorious detention centres in the capital, N'Djamena, while Amnesty reports that some political prisoners were held at the presidential palace.
Survivors said the most common forms of torture were electric shocks, near-asphyxia, cigarette burns and having gas squirted into the eyes.
Sometimes, the torturers would place the exhaust pipe of a vehicle in their victim's mouth, then start the engine, Amnesty says.
Some detainees were placed in a room with decomposing bodies, other suspended by their hands or feet, others bound hand and foot.
One man said he thought his brain was going to explode when he was subjected to "supplice des baguettes" (torture by sticks), when the victim's head is put between sticks joined by rope which are then twisted.
Others were left to die from hunger in the "diete noire" (starvation diet).
HRW says that members of any ethnic group seen as being opposed to Mr Habre were targeted: the Sara in 1984, the Hadjerai in 1987 and Chadian Arabs and the Zaghawa in 1989-90.
Mr Habre was eventually deposed by current President Idriss Deby, an ethnic Zaghawa, who has been accused of favouring members of his own community.
After being ousted, he fled to exile in Senegal, where he has kept a low profile.
He has however, become involved with the local Tijaniyya Islamic sect and four of his children were born there.
"I can say that my children don't know Chad. Their country is Senegal," Mr Habre's wife, Fatime Raymonde, told a local newspaper.
His alleged victims, backed by Human Rights Watch, have tried to bring him to justice ever since but have repeatedly been thwarted.
First, a Senegalese court refused to put him on trial, saying it did not have jurisdiction over alleged crimes committed in Chad.
Senegalese President Abdoulaye Wade gave Mr Habre a month to leave the country but the UN intervened, in case the former Chad leader found a country where he would be safe from prosecution.
Senegal was told to prevent Mr Habre from leaving its territory.
Last year, a Belgian court issued an arrest warrant, based on its universal law which lets Belgium try those accused of human rights abuses wherever they are committed.
Mr Habre was then arrested but again, a Senegalese court sided with Mr Habre's lawyers and refused to extradite him to Belgium.
Now, Africa's leaders have agreed to set up a special court to try him - again in Senegal.
Chadian victim's group are hoping it will be third time lucky and Mr Habre will finally answer for the murders and torture allegedly carried out in his name.