He won Tonys for his orchestrations and Grammys for his compositions and arrangements. But he was best known for his genre-straddling work at CTI Records.Don Sebesky, who in a wide-ranging musical career played with leading big bands, was a behind-the-scenes force at CTI Records and other jazz labels, won Grammy Awards for his own compositions and arrangements, and orchestrated some 20 Broadway shows, died on April 29 at a nursing home in Maplewood, N.J. He was 85.The cause was complications of dementia, his daughter Elizabeth Jonas said.Mr. Sebesky’s musical interests ranged far and wide. He created arrangements not only for jazz musicians but also for a diverse range of pop vocalists, including Nancy Wilson, Roberta Flack, Rod Stewart and Barry Manilow. To jazz aficionados, though, he was best known — and sometimes criticized — for the work he did as a sort of house arranger for Creed Taylor Inc., better known as CTI, a jazz label that was a major force in the 1970s.From the beginning, Mr. Taylor and CTI were on a mission to broaden the audience for jazz by exploring intersections with pop, rock and R&B, and by making music that was more accessible to mainstream audiences than some of jazz’s more esoteric strains. It was an approach that displeased some purists, but it sold records, and Mr. Sebesky’s arranging skills were pivotal to that success.Mr. Sebesky arranged the saxophonist Paul Desmond’s “Bridge Over Troubled Water” (1970), an album of interpretations of Simon & Garfunkel songs. He arranged the guitarist George Benson’s “White Rabbit” (1972), an album anchored by Mr. Benson’s rendition of the title track, the psychedelic Jefferson Airplane hit. Pairing Mr. Benson with that song was an idea Mr. Sebesky had proposed to Mr. Taylor, but with a twist.“I suggested we do ‘White Rabbit’ in a Spanish mode,” Mr. Sebesky told Marc Myers for the website JazzWax in 2010. “He agreed. George Benson doesn’t read music. He just heard the song and automatically fell into the groove.”Mr. Sebesky in the studio with the pianist Herbie Hancock and the guitarist Wes Montgomery in 1967, working on Mr. Montgomery’s album “A Day in the Life.” The album would be one of the most successful Mr. Sebesky arranged.Chuck StewartThose were just two of the countless records on which Mr. Sebesky worked for CTI from the late 1960s (when it was a subsidiary of A&M) through the 1970s. He also made his own albums as a bandleader, for CTI and other labels. These, too, often merged jazz and rock.His debut album, “The Distant Galaxy” (1968), included versions of Bob Dylan’s “Mr. Tambourine Man” and the Beatles’ “Lady Madonna.” “Don Sebesky and the Jazz-Rock Syndrome,” released the same year, included his version of the Peter, Paul and Mary hit “I Dig Rock and Roll Music” as well as other covers.In 1984 Mr. Sebesky made his nightclub debut as a bandleader, bringing a 12-piece band to Fat Tuesday’s in Manhattan to play selections from “Full Cycle,” an album he had just released on the Crescendo label that featured his arrangements of Miles Davis’s “All Blues,” John Lewis’s “Django” and other jazz standards.“At Fat Tuesday’s, a low-ceilinged, narrow room in which the 12 musicians must be strung out in a line, instrumental separation and clarity are a far cry from the possibilities of a recording studio,” John S. Wilson wrote in a review in The New York Times. “But what may be lost in this respect is made up for in the vitality and involvement projected by the musicians and the visual razzle-dazzle of the variety of instruments brought into play.”The next year, reviewing a return engagement at the same club, Mr. Wilson wrote, “This is a band full of fresh ideas and fresh sounds that set it apart.”By then, Mr. Sebesky had begun working on Broadway as well. His first credit was for some of the orchestrations for “Peg,” a 1983 autobiographical one-woman show starring the singer Peggy Lee.That show was short-lived, but many of his other Broadway shows did better. The 1999 revival of “Kiss Me, Kate” ran for more than two years and won him a Tony Award for best orchestrations. “An American in Paris” in 2015 also had a long run, and he shared a second Tony, with Christopher Austin and Bill Elliott, for the orchestrations of that show.His one attempt at writing the score for a Broadway show was less successful. “Prince of Central Park,” for which he wrote the music and Gloria Nissenson wrote the lyrics, closed after four performances in 1989.In 1999 Mr. Sebesky, after many nominations, won his first Grammy Award, for his arrangement of the pianist Bill Evans’s “Waltz for Debby” on his album “I Remember Bill: A Tribute to Bill Evans.”The next year was a career highlight: He became one of the few people who could say that he didn’t lose a Grammy to Carlos Santana.Mr. Santana, thanks to his album “Supernatural,” was a Grammy juggernaut that year, winning eight awards. In the category of best instrumental composition, Mr. Sebesky won for “Joyful Noise Suite” — beating out, among others, Mr. Santana.“That was very much of a surprise,” Mr. Sebesky, who also won a Grammy that year for best instrumental arrangement, told The Home News Tribune of New Jersey in 2000. “We expected the Santana steamroller to run over everything.”Mr. Sebesky played accordion on the guitarist and singer John Pizzarelli’s 1998 album of Beatles songs. “My mother,” he once said, “thought I’d be the best accordion virtuoso in the Western Hemisphere.” But he had other plans.via Sebesky familyDonald Alexander Sebesky was born on Dec. 10, 1937, in Perth Amboy, N.J. His father, Alexander, was a laborer in a steel cable factory, and his mother, Eleanor (Ehnot) Sebesky, was a homemaker.He studied composition at the Manhattan School of Music but left before graduating in the late 1950s to pursue a nascent career as a trombonist, playing in the bands of Stan Kenton and Maynard Ferguson.Before studying with the big-band trombonist Warren Covington, his instrument had been the accordion.“My mother was real disappointed” when he switched instruments, he told The Evening Press of Binghamton, N.Y., in 1982. “She thought I’d be the best accordion virtuoso in the Western Hemisphere.”By the early 1960s, Mr. Sebesky was concentrating on writing and arranging.“There seemed like nothing could be better than taking a group of instruments and seeing what sounds could be made to come out of them,” he told The Evening Press.Mr. Sebesky’s first marriage, to Janet Sebesky, ended in divorce. He married Janina Serden in 1986. In addition to Ms. Jonas, his daughter from his second marriage, he is survived by his wife; another daughter from his second marriage, Olivia Sebesky; two sons from his first marriage, Ken and Kevin; a brother, Gerald; and nine grandchildren. Two daughters from his first marriage, Cymbaline Rossman and Alison Bealey, died before Mr. Sebesky. Before moving to the nursing home in Maplewood, he lived for about 30 years in Mendham, N.J.Jamie Lawrence, an Emmy Award-winning musician and music director who worked with Mr. Sebesky on various projects, including playing synthesizer on demos for commercials Mr. Sebesky worked on, recalled that Mr. Sebesky’s charts could be hard to read — a result, he thought, of his working quickly because he always had so many jobs going on.“But if you could decipher them and get all the notes down,” he said in a phone interview, “they all made sense. They were the right notes. He was a musician’s musician.”Alex Traub More