The Serbian ultra-nationalist leader, Vojislav Seselj, has been accused of inciting forces with "poisonous ideas" at the start of his war crimes trial.
Vojislav Seselj surrendered to the ICTY in February 2003
Prosecutors at The Hague said speeches he made during the wars in Bosnia and Croatia in the 1990s led to the murder, torture and persecution of non-Serbs.
Mr Seselj, the leader of the Serbian Radical Party, has denied the charges.
He has said he will rely on a political defence and use the tribunal to show there is a conspiracy against Serbia.
Mr Seselj surrendered to the ICTY voluntarily in February 2003, vowing to clear his name of three charges of crimes against humanity and six counts of war crimes, including persecution, deportation, murder and torture.
However, he remained the figurehead of the Serbian Radical Party (SRS) while awaiting trial and was elected one of its members of parliament in the January 2007 election.
The SRS subsequently became the biggest party in parliament, but was kept out of power by a coalition of reform-orientated parties.
Dressed in a dark suit and flanked by two guards, the 53-year-old appeared relaxed and confident at the start of his trial at the International Criminal Tribunal for the former Yugoslavia (ICTY).
In her opening statement, prosecutor Christine Dahl accused the former close associate of the late Serbian leader, Slobodan Milosevic, of making several inflammatory speeches calling for the creation of a "Greater Serbia".
She said hundreds of people were tortured and killed by Serb forces, who had been recruited or indoctrinated by Mr Seselj with "poisonous ideas" and sent to commit "unspeakable crimes" in Bosnia and Croatia.
Ms Dahl then told the story of a Bosnian Muslim woman who was raped by Serbs and whose husband and two young children were killed.
"The destruction of her community, her life, her family exemplifies the product of the belligerent, bellicose nationalism propagated by the accused," she told the tribunal's three judges.
Both he and Milosevic planned to ethnically cleanse large parts of the former Yugoslavia, Ms Dahl alleged, "but while Milosevic would not dare call aloud for the liberation of Serb territory, Seselj would, and did".
1954: Born in eastern Herzegovina
1984: Jailed for criticising Communists
1990: Sets up Serbian Radical Party (SRS)
1991: Elected to Serbian Assembly
1993: Forces dissolution of Serbian parliament
1999: Resigns as vice-president in Serbian Government
2002: Stands in Serbian presidential elections
2003: Indicted by UN war crimes tribunal
2007: War crimes tribunal opens at The Hague
"In the end, Mr Seselj did not achieve a Greater Serbia. He only managed to achieve a lesser Serbia, and gave the world the phrase 'ethnic cleansing'," she added.
The defendant chuckled when the prosecutor recounted the story of his dismissive reaction when he was told of atrocities committed by one of his volunteers.
"What can I do, he's tired - take his guns and send him home," Ms Dahl quoted him as saying.
Mr Seselj, who like Milosevic is acting as his own lawyer and displays contempt for the court, does not deny making nationalist speeches, but insists they do not constitute war crimes.
"I am being tried for atrocious war crimes that I allegedly committed through hate speech as I preached my nationalist ideology that I am proud of," he said at a pre-trial hearing on Tuesday.
"I have no other involvement in these crimes except for what I said or wrote."
He is due to make his opening statement on Thursday.
Mr Seselj's trial began a year ago, but was almost immediately stopped when he went on a hunger strike for 28 days to push various demands, including that he be able to defend himself.
Other key war crimes suspects, former Bosnian Serb leader Radovan Karadzic and his military chief, Gen Ratko Mladic, remain at large.
Milosevic died in detention in The Hague in March 2006 before his war crimes trial ended.
The BBC's Nick Hawton in Belgrade says Mr Seselj still has influence over political developments in Serbia.
MPs from his party turn up to debates wearing t-shirts or badges with his face emblazoned on them.
The SRS may not be in power, but political stability in Serbia is fragile and with the sensitive issue of Kosovo still to be resolved and a presidential election expected in the next two months, the party could benefit from the trial of their leader, our correspondent says.
Serbian state television has agreed to broadcast substantial parts of the trial, which is expected to last for about a year.
Many people will watch, either for the political rhetoric that Mr Seselj is sure to produce, or for the colourful and dismissive language that he employed in many of the pre-trial hearings, our correspondent adds.