A UN-backed tribunal has convicted Theoneste Bagosora, a former Rwandan army colonel, of organising the 1994 genocide in Rwanda.
Two other former military officers were also convicted by the International Criminal Tribunal for Rwanda on Thursday for their role in the mass killings of minority Tutsis and moderate Hutus.
"Colonel Bagosora is guilty of genocide and crimes against humanity and war crimes," the court said.
The tribunal, based in Arusha, Tanzania, accused Bagosora of leading the troops and Interahamwe Hutu fighters that carried out the killings, which left an estimated 800,000 dead.
Prosecutors said Bagosora, formerly a cabinet director in the defence ministry, assumed control of military and political affairs in Rwanda after Juvenal Habyarimana, then Rwanda's president, was killed when his plane was shot down.
Bagosora was said to have stormed out of peace talks in Tanzania saying he was returning to Rwanda to "prepare the apocalypse".
'Brutal and racist'
Linda Melvern, a journalist and a consultant for the International Criminal Tribunal for Rwanda, told Al Jazeera that Thursday's convictions would "mean a lot for the people of Rwanda".
Born on August 16, 1941 in Rwanda's Gisenyi prefecture, the region home to many of the country's former Hutu elite.
Graduated as an officer in 1964 and later went for advanced military studies at a French staff college. He retired from the army in 1993 but remained at his post in the defence ministry.
After the genocide, Bagosora fled into exile in Cameroon where he was arrested in 1996.
His trial began in 2002.
Romeo Dallaire, who led UN peacekeepers during the Rwanda genocide, described Bagosora as the "kingpin" behind the killings and said that the colonel had threatened to kill him with a pistol.
"We can only hope that life [in prison] will mean life and wherever he [Bagosora] serves his sentence there is a guarantee that he will be secure ... The genocide was extraordinarily brutal and these convicts are the most brutal, brutal, racist people."
But she said that many of those who played roles in the killings had yet to be brought to justice.
"The original list that I have of category one perpetrators - those who financed and organised the genocide - has some 240 names, so there are very many genocidaires who are still at large," she said.
Kennedy Ndahiro, the editor of the Rwandan daily newspaper The New Times, told Al Jazeera: "The mood here is that something is being seen to be done after 14 years of waiting."
But Ndahiro said that generally the view in Rwanda is that the tribunal has been "very lazy" in taking so long to begin convicting those culpable.
Earlier the tribunal found Habyarimana's brother-in-law Protais Zigiranyirazo, known as "Monsieur Z", guilty of genocide and sentenced him to 55 years in prison.
Zigiranyirazo was accused of being a member of the Akazu, the ruling elite of Hutu family members and relatives who are believed to have plotted to exterminate the minority Tutsis.
He was said to have been a member of the notorious Zero Network of death squads which killed hundreds of Tutsis and opposition leaders in the years leading up to the genocide.
Prosecutors said Zigiranyirazo sanctioned roadblocks to be set up near his three residences and paid for a mass grave to be dug outside his compound to bury those killed.
Zigiranyirazo was also said to have armed, trained and clothed the Interahamwe fighters who conducted most of the killings.
The court began its work in 1997 and has until the end of the year to wind up its activities and until 2010 to hear all appeals.
The UN General Assembly is discussing whether to extend the court's mandate.