Mr. Mortier was that company’s artistic director from 2009 until last year, when his title was changed to artistic adviser in a tussle with the Spanish government over his successor, after he announced in September that he was being treated for cancer.
It was a characteristic dispute for a man who always relished a battle during a four-decade career at the helm of some of the world’s most important opera companies, including the Salzburg Festival and the Paris Opera.
Sometimes the grounds were artistic, as in the furor over his farewell production after 10 years in Salzburg: a 2001 “Die Fledermaus” taking aim at the Austrian government and featuring drugs and Nazi thugs.
Sometimes they were financial, as when the Théâtre de la Monnaie in Brussels, which he led from 1981 to 1991, went into debt over his lavish renovation of the opera house, complete with a floor by the American Minimalist artist Sol LeWitt.
And sometimes they related to Mr. Mortier himself, as when he and New York City Opera parted ways in 2008, a scant year and a half into his tenure.
These clashes were less tantrums than expressions of his bracing, intellectually charged vision of opera and his disdain for the decorous irrelevance often associated with it. In the summer of 2011, reflecting in an interview on a raucous Madrid production of Karol Szymanowski’s “King Roger” the previous fall, he said with a smile: “It was an enormous scandal, and it became an enormous success. On opening night, I said, ‘Now we are really international.’ People aren’t sleeping at the end.”
Gerard Alfons August Mortier was born on Nov. 25, 1943, in Ghent, Belgium, where his parents owned a bakery in a working-class neighborhood. His mother and grandmother took him to the opera as a child, and at home he would stage Mozart’s “Magic Flute” in a puppet theater.
He said he had acquired his taste for controversy at a boarding school run by the Jesuits, who had him and his classmates read iconoclastic writers like Marx, Nietzsche, Ibsen and Sartre. In 1968, as students protested throughout Europe, Mr. Mortier formed a group of young opera fans that loudly jeered productions it judged overly conservative.
After receiving graduate degrees in law and communications, he took a job as an assistant at the Festival of Flanders. There he met the conductor and impresario Christoph von Dohnányi, who was making innovative music theater at the Frankfurt Opera. Mr. von Dohnányi took Mr. Mortier to Frankfurt as an assistant, and then with him to positions in Hamburg and Cologne.
Mr. Mortier went on to his first stint at the Paris Opera as an assistant to Rolf Liebermann, who was revitalizing the company’s artistic mission with 20th-century operas like Schoenberg’s “Moses und Aron” and untraditional productions focused on contemporary relevance, as part of the dawn of the era of director-driven Regietheater.
It was a style of cerebral showmanship that Mr. Mortier echoed in his first major appointment, at the Théâtre de la Monnaie. That opera house had been a backwater, but he gave it new energy, showcasing a stark version of Verdi’s “Don Carlo,” Herbert Wernicke’s influential one-set take on Wagner’s “Ring” cycle, the premiere of John Adams’s “Death of Klinghoffer” and the operas of Janacek.
When the Belgian choreographer Maurice Béjart resigned as the theater’s longtime dance director in 1987, Mr. Mortier appointed the young American Mark Morris, who created masterpieces like “Dido and Aeneas” and “L’Allegro, il Penseroso ed il Moderato.” But Mr. Mortier did not renew his contract after three years of tumultuous responses from conservative audience members and critics.
Shortly after Mr. Morris left, Mr. Mortier did, too, succeeding the late Herbert von Karajan as the director of the Salzburg Festival. There he faced a well-heeled public possibly even more tradition-bound than the one in Brussels, but he gave them challenging fare, nonetheless.
Classic operas got stimulating makeovers, not excluding Salzburg’s beloved Mozart: a “Marriage of Figaro” was set in a seedy Eastern European wedding boutique, and Achim Freyer’s version of “The Magic Flute” turned the characters into clowns in a celestial circus.
Peter Sellars directed searching productions of Ligeti’s “Le Grand Macabre” (1978) and Messiaen’s “St. François d’Assise” (1983), two operas that have entered the international repertory in no small part because of Mr. Mortier’s advocacy. He also commissioned new works, like Kaija Saariaho’s “L’Amour de Loin.”
He left in 2001 amid a rightward turn in Austrian politics, and helped found the RuhrTriennale arts festival in an ex-industrial corner of Germany.
In 2004 he took over at the Paris Opera, one of the biggest and richest companies in the world. There he brought back “St. François d’Assise” and introduced a shimmering Robert Wilson production of Debussy’s “Pelléas et Mélisande,” gritty work by the director Christoph Marthaler and Mr. Sellars, and Bill Viola’s video-dominated version of Wagner’s “Tristan und Isolde.”
In 2007, approaching the mandatory retirement age of 65, Mr. Mortier was hired as the general manager and artistic director of New York City Opera, a coup for a scrappy company that had long labored in the shadow of the Metropolitan Opera, a few yards away.
City Opera went ahead with Mr. Mortier’s plan to close and renovate its Lincoln Center home during the 2008-9 season as he commuted between New York and Paris. The idea was that the quality and audacity of the new productions would stimulate giving. Until then, dipping into the company’s endowment would tide it over, coupled with a push from the board.
But board members were disturbed in the summer of 2008, when Mr. Mortier joined in a failed proposal to run the Bayreuth Festival in Germany. He later said that he knew the proposal would be rejected, and that he was trying to send a message to City Opera as he increasingly doubted its commitment to his plans.
Conditions worsened after the economic downturn began in earnest that fall. Mr. Mortier was presented with a $36 million budget for his first season, little more than half of what he had agreed to. He balked.
“I cannot go to run a company that has less than the smallest company in France,” Mr. Mortier said. “You don’t need me for that.”
A few months earlier, Teatro Real had called to gauge his interest in a job. He demurred. The day he and City Opera parted ways, the company called again, and three weeks later he agreed to take the position in Madrid.
His tenure began with Emilia and Ilya Kabakov’s sprawling production of “St. François d’Assise,” held in a cavernous basketball arena, and continued with an ambitious first season, the operas of Verdi and Puccini conspicuously absent.
In the following years, he brought to Madrid commissions he had intended for New York, including Philip Glass’s “Perfect American” and Charles Wuorinen’s “Brokeback Mountain,” which opened in January, programmed — in typically clever Mortier fashion — in repertory with “Tristan und Isolde,” another tale of impossible love.
He is survived by his sister, Rita Mortier. Mr. Mortier was a generous and powerful mentor, many of whose former assistants, dramaturges and casting advisers have risen to prominence themselves, including Peter de Caluwe, the current head of the Théâtre de la Monnaie; and Alexander Neef, the director of the Canadian Opera Company in Toronto. Like Mr. Mortier, they have made a priority of creating opera that moves audiences to ask questions about their lives and society.
“We are working every day to defend the same things he spent his career defending,” Mr. de Caluwe said in a phone interview.
While Mr. Mortier savored the parries and thrusts of that defense, he never considered the provocations for which he was famous an end in themselves. Mr. de Caluwe recalled a line he loved to repeat: “If controversy creates tension, tension creates friction, and friction creates warmth. And warmth is what I’m looking for.”
