Chad's ex-President Hissene Habre has been charged in Senegal with war crimes, crimes against humanity and torture by a special court.
The 70 year old, who was arrested on Sunday in the Senegalese capital, Dakar, denies killing and torturing tens of thousands of his opponents.
He fled to Senegal when he was deposed after eight years in power in 1990.
Last year, the UN's International Court of Justice ordered Senegal to put him on trial or extradite him.
Mr Habre appeared before a special court set up in Senegal to investigate the allegations. He will remain in custody pending the trial.
Analysts say the case would be a milestone for African justice - representing the first time an African leader has been tried in a fellow African country on charges of crimes against humanity.
The Senegalese authorities and the African Union had for years failed to make a decision on his fate despite pressure from human rights groups.
Mr Habre and his wife kept a low profile in Dakar, where he lived in relative freedom despite being put under house arrest in 2005 - guarded by two security agents.
Senegalese MPs passed a law in December allowing a special African Union tribunal to be created in the country to try the former leader, who has been dubbed "Africa's Pinochet".
The BBC's Thomas Fessy in Dakar says the official investigation will take up to 15 months before a trial can start.
The charges against him date from 1982, when Mr Habre came to power in a coup, until 1990, the year he was ousted.
Jacqueline Moudeina, a lawyer for some of his alleged victims, told the BBC that the move came as a relief to her clients who had been seeking justice for years.
Mr Habre's lawyer El-Hadji Diouf told the BBC he remained confident the truth would eventually emerge and Mr Habre would be discharged.
The former Chadian president was first indicted in Senegal in 2000 - but the country's courts ruled at the time that he could not be tried there.
His alleged victims then filed complaints under Belgium's universal jurisdiction law, which allows the country's judges to prosecute human rights offences committed anywhere in the world.
He was charged by Belgium with crimes against humanity and torture in 2005, but Senegal has refused four extradition requests.
Plans in 2011 to repatriate Mr Habre to Chad, where a court in 2008 sentenced him to death in absentia for planning to overthrow the government, were stopped following a plea from the UN.