His death came after a long battle with cancer, his wife, Sylvia, said.  In books, law journals and decisions from the bench, Judge Cassese expanded the body of international law that had lain mostly dormant since the trials at Nuremberg and Tokyo after World War II.  A professor of law in Florence and Oxford early in his career, in 1993 he became the first president of the International Criminal Tribunal for the former Yugoslavia, a court established by the United Nations to deal with war crimes in the Balkans in the 1990s.  He proved to be something of a maverick among normally discreet justices. Invariably affable but outspoken, he prodded fellow lawyers and Western governments into providing more support for the fledgling tribunal. And he played a central role in defining rules that would guide it and that have since served as a model for other tribunals and courts.  Among his early decisions, seen as controversial at the time but widely accepted since, were several that changed basic precepts of international criminal law. One was that war crimes could be punished not only in wars between nations, but also in conflicts within a particular country. In another, he wrote that even if there was no war going on, massacres, torture and other atrocities committed by governments or groups could be found to be crimes against humanity and punished accordingly.  “Perhaps more than any other person, Antonio Cassese was both the visionary and the architect of international criminal justice,” said Theodor Meron, an American judge who will take over next month as president of the Yugoslavia tribunal.  Most recently, Mr. Cassese was president of the Special Tribunal for Lebanon, created by the United Nations to try those accused of killing Lebanon’s former prime minister Rafik Hariri and 22 others. He stepped down as president two weeks ago, as his health was failing.  Over the years, Mr. Cassese became a familiar figure in The Hague, where several international courts are based. He was often seen riding his bicycle, and he was popular with colleagues for his wit and personal modesty, as well as his erudition.  Claude Jorda, a former judge from France at the Yugoslavia tribunal, recalled that when Mr. Cassese arrived in The Hague, he was a great legal scholar, with no idea what it meant to be a judge. “But he did know that the new tribunal was the one and perhaps only chance to make international justice work,” Judge Jorda said, adding, “Failure was unthinkable to him.”  Stephen J. Rapp, the United States ambassador for war crimes and a former international prosecutor who knew Mr. Cassese for many years, said, “Everywhere that he served, Judge Cassese was the energetic force that overcame inertia, caution and resistance in order to work for justice for the victims of the most serious crimes known to humankind.”  Born Jan. 1, 1937, in Atripalda, a town in a poor region of southern Italy, he had hoped to study philosophy or sociology but instead opted for law. He said his father, whom he once described as an impecunious civil servant, urged him to pursue a more secure career. A bonus was that he was offered free board and lodging at the University of Pisa if he studied law.  In an essay called “Soliloquy,” a personal history, he wrote that he initially found it difficult to learn the hard discipline and the rigorous logic of law. But eventually he became known for scholarly work ranging from numerous essays to books including “The Tokyo Trial and Beyond: Reflections of a Peacemonger,” based on his conversations with a Dutch judge, B. V. A. Roling.  He was editor in chief of the more than 1,000-page “Oxford Companion to International Criminal Justice” and founded the Journal of International Criminal Justice, which became a prestigious forum for debate.  He insisted on the need for continuous debate because international law was gradually emerging, and as such, reflecting the common conscience of mankind. But he said it was vital to remain skeptical about harsh laws. “Laws may and should be improved if they are not up to reality,” he said frequently.  To remind himself, he kept these words from Bertolt Brecht, the German playwright and poet, on his office wall in The Hague: “I am by nature a man who is difficult to control. I reject with outrage any authority that does not rest on my respect. And I regard laws only as provisional and changeable proposals for regulating human intercourse.”  He won numerous awards for his work, including the the 2009 Erasmus Prize in the Netherlands. He used the prize money to help law students publish their papers.  He is survived by his wife and their son and daughter and two grandchildren.  In 2004, Mr. Cassese headed the United Nations Commission of Inquiry on Darfur, which led the Security Council to ask the International Criminal Court to open a criminal investigation of the reported large-scale crimes against civilians. The court eventually issued an arrest warrant for several officials from Sudan, including the country’s president, Omar Hassan al-Bashir.  Mr. Cassese could be critical of fellow judges whom he thought lazy or inefficient. In a 2006 report on the Special Court for Sierra Leone, he charted the number of hours the judges were working and said that they were taking too many breaks.  Patricia M. Wald, a former federal judge in the Unites States, who was an appeals judge on the Yugoslavia tribunal, recalled the time that her appeals panel overturned a judgment and acquitted four defendants convicted by a bench that included Mr. Cassese.  “He was most gracious about it afterwards, and even invited me to write for his law journal,” Judge Wald said. She added that he turned his knowledge into concrete action that became the bedrock for several international courts.  “There are moments in history when one individual can make a great difference, and he was such a man,” Judge Wald said.  This article has been revised to reflect the following correction:  An obituary on Monday about Antonio Cassese, who helped found two international war crimes tribunals, misstated the publication schedule of The Journal of International Criminal Justice, which he founded. It is published five times a year, not monthly.  An obituary on Monday about Antonio Cassese, who helped found two international war crimes tribunals, misstated the publication schedule of The Journal of International Criminal Justice, which he founded. It is published five times a year, not monthly.
The founder of two war-crimes tribunals, Mr. Cassese played a vital role in creation of a modern system of international criminal justice.