Bruno Bartoletti, an Italian conductor long associated with the Lyric Opera of Chicago, died June 9, 2013, in Florence. (Peter Koeleman/Courtesy of Lyric Opera of Chicago)

Bruno Bartoletti, an Italian conductor who helped transform the Lyric Opera of Chicago into one of the most respected and daring opera companies of its kind, died June 9 in Florence. He was 86.

The Lyric Opera announced his death but did not cite a specific cause.

Mr. Bartoletti was 30 when he flew to the United States to make a hastily planned U.S. debut in Chicago in 1956. The fledgling Lyric Opera sorely needed a conductor to replace the ailing maestro Tullio Serafin in several performances. Tito Gobbi, the acclaimed Italian baritone, put in a word for the young Mr. Bartoletti.

His debut — in Verdi’s “Il Trovatore” — would be the first of nearly 600 performances of 55 operas with the Lyric Opera over the next five decades. Mr. Bartoletti was named the company’s co-artistic director, with Pino Donati, in 1964 and became the sole artistic director in 1975.

He remained associated with the Lyric Opera after his official retirement in 1999, bringing to the Chicago music scene a degree of constancy rarely found in the tumultuous opera world.

“I cannot make music like my colleagues do, rushing from this theater to that theater all over the world, conducting a different opera every week,” he told the Chicago Tribune. “To present opera beautifully takes time. And love.”

Mr. Bartoletti was known as an insightful interpreter of the Italian canon, including works by Verdi and Puccini. But he also expanded the Lyric Opera’s repertoire to include a range of modern works, helping the Midwestern opera company establish an international reputation for its musical ambition.

The Lyric Opera credited Mr. Bartoletti with bringing to the company modern operas including Berg’s “Wozzeck,” Prokofiev’s “The Fiery Angel” and “The Gambler,” Britten’s “Billy Budd,” Bartok’s “Bluebeard’s Castle” and Janacek’s “The Makropulos Case.” He conducted the 1978 world premiere of Krzysztof Penderecki’s “Paradise Lost,” a production that drew attention for its extravagant expense and that was reported to have pushed the company into financial crisis.

“Everywhere I go — Florence, Milan, Munich — the reaction is the same,” Mr. Bartoletti told the Tribune in 1990. “Opera people are very impressed, somewhat surprised and a little envious that all this should be happening in Chicago.”

Mr. Bartoletti directed some of the leading opera singers of his era, including Placido Domingo, Luciano Pavarotti, Marilyn Horne, Grace Bumbry, Jussi Bjorling, Renata Tebaldi, Mirella Freni, Montserrat Caballé and Giuseppe Di Stefano, according to the Lyric Opera. Mr. Bartoletti was described as a complement to their vocal talents and to the operas themselves.

“Bruno Bartoletti’s conducting was so thoroughly idiomatic it never drew attention to itself, but effectively served the story’s unfolding,” music critic Edward Rothstein wrote in the New York Times in 1991, reviewing a performance of “The Gambler.”

Bruno Bartoletti was born June 10, 1926, in Sesto Fiorentino, Italy. He studied the flute and piano before pursuing conducting as his career, initially at Florence’s Teatro Comunale in the years after World War II. His most important mentors included Serafin.

Mr. Bartoletti conducted around the world, including in Rome, at London’s Royal Opera House in Covent Garden, at the Teatro Colon in Buenos Aires and, for many years, at the Maggio Musicale festival in Florence. Once, reflecting on his career, he described it as “a very long symphonic poem.”

Mr. Bartoletti’s wife of 58 years, the former Rosanna Sandretti, died in 2011. Survivors include two daughters, Chiara Bartoletti and Maria Poggi; a sister; a brother; and five grandchildren.

Mr. Bartoletti was known for his even temper in a profession known for attracting more volatile types of talent. He once joked about the melodrama that sometimes surrounds opera companies and the divas who grace their stages.

“Opera is sometimes messy,” he remarked. “That’s because opera is life.”