An experimental composer, Mr. Deutsch collaborated with Robert Moog to create the first synthesizer to make a significant impact on popular music, launching a revolution in electronic music.Herbert Deutsch, who helped develop the Moog synthesizer, a groundbreaking instrument that opened up new frontiers in electronic music and brought a futuristic sheen to landmark recordings by countless artists, died on Dec. 9 at his home in Massapequa Park, N.Y., on Long Island. He was 90.The cause was heart failure, his wife, Nancy Deutsch, said.Mr. Deutsch, a Hofstra University music professor and experimental composer, joined forces with Robert Moog, an engineer and inventor, to introduce a modular voltage-controlled synthesizer in 1964.With its otherworldly sounds, which could call to mind both a Gothic cathedral’s pipe organ and an extraterrestrial mothership, the Moog (the name rhymes with “vogue”) was the first synthesizer to make a significant impact on popular music. Its debut marked the dawn of the synthesizer age.“There were plugged-in instruments before the Moog synthesizer, but none arrived on the scene with such awe-inspiring potential,” Ted Gioia, the music writer and author of the 2019 book “Music: A Subversive History,” wrote in an email. “The first recordings of Moog music from the 1960s felt like messages from the future, telling us that all the rules were going to change.”Many of those recordings turned out to define their eras. George Harrison purchased an oversized early Moog, which the Beatles used to color multiple tracks on their 1969 album, “Abbey Road,” including “Maxwell’s Silver Hammer” and Harrison’s composition “Here Comes the Sun.”The Moog reached a broader market in 1971 with the introduction of the compact Minimoog Model D, the first widely used portable synthesizer.“Within months of the first commercial Moog synthesizers showing up in retail stores, commercial recordings started to sound different,” Mr. Gioia said. The futuristic synthesizer beeped and booped its way onto the pop charts in 1972 with “Popcorn” by Hot Butter, and went on to become a driving force behind landmark songs like Kraftwerk’s arty “Autobahn,” Donna Summer’s disco classic “I Feel Love” (1977), Parliament’s epic funk freak-out “Flashlight” (1977) and Herbie Hancock’s jazz-funk crossover hit “Rockit” (1983).The Minimoog Model D, introduced in 1971, was the first widely used portable synthesizer.Moog Music Inc.Even when it was not the featured instrument, the Moog provided moody textures to timeless songs like Bob Marley’s “Stir It Up” (1973) and Pink Floyd’s “Wish You Were Here” (1975). It also provided throbbing bass tracks to Michael Jackson’s mega-selling 1982 album, “Thriller.”While Mr. Moog handled the technical side of his namesake invention, during its creation Mr. Deutsch provided a practicing musician’s perspective, which was crucial in transforming it from an electronic gadget into a viable instrument.“Herb Deutsch was the catalyst for the invention of the synthesizer,” Michelle Moog-Koussa, Mr. Moog’s daughter and the executive director of the Bob Moog Foundation, said in a phone interview. “That is no overstatement.”“Herb would say, ‘This is what I need,’” she added, “and Dad would build the circuitry. It was a true partnership between a designer and a musician.”Despite his impact on music of all genres, Mr. Deutsch was the last person to trumpet his accomplishments.“I’m unwilling to go around shouting, ‘Look at me, I’m a part of the history of music,’” he said in a video interview with the Moog Music company in February. “But I do understand that Bob and I are an important part of music history, because that idea has been used in every direction that music can go into.”Herbert Arnold Deutsch was born on Feb. 9, 1932, in Hempstead, N.Y., the youngest of three children of Barnet and Miriam (Myersburg) Deutsch. His father was a clerical worker for the Veterans Health Administration, his mother a bookkeeper. With money tight, his parents also ran a small chicken farm on their property.In a detached garage next to the farm’s largest coop Mr. Deutsch, at age 3, had his first musical epiphany.“For some reason, I had picked up a long straight stick and, holding it in my right hand, was tapping it down on the dirt floor,” he recalled in a 2018 interview with Parma Recordings, a music production company. “At some point in this meaningless action I heard a note whenever I tapped the floor.”“It was a C,” he continued. “Then I tapped the floor an inch or so to the right and heard a D.”Soon he began to “tap out some melodies of music that I recognized as well as music that was new to me,” he said. “Suddenly, I stopped in terror. Of course I could not hear those actual pitches, or was the dirt floor truly magical?”The German rock band Kraftwerk was among the earliest exponents of the Moog synthesizer.Gie Knaeps/Getty ImagesHe started piano lessons a year later, and at 11, inspired by the likes of Louis Armstrong and Dizzy Gillespie, turned his sights to the trumpet. He played in bands throughout high school and during his years at the Manhattan School of Music, where he earned bachelor’s and master’s degrees.One of his best-known compositions was the haunting, multi-media track “A Christmas Carol, 1963,” an aural collage interspersed with recorded news snippets and medieval chants composed to honor the four Black girls murdered in the infamous Ku Klux Klan bombing of a church in Birmingham, Ala., that year.His performance of another modernist composition at the New York studio of the sculptor Jason Seley in January 1964 earned a positive review in The New Yorker. More significant, however, was the fact that Mr. Moog was in the audience.Mr. Moog, whom Mr. Deutsch had met at a music trade show, was working on his Ph.D. in engineering physics at Cornell University while running the small R.A. Moog Company, based in Trumansburg N.Y., which manufactured his versions of the theremin, the electronic instrument whose eerie space-age sound was a staple of 1950s science-fiction movie soundtracks.After the performance, the men and their wives went to dinner, where Mr. Deutsch and Mr. Moog discussed new possibilities for electronic music. Mr. Deutsch ended up commissioning a new electronic instrument, to be designed by Mr. Moog in collaboration with Mr. Deutsch.With Mr. Deutsch advising, Mr. Moog designed an instrument consisting of modules linked by patch cords that allowed musicians to create their own vast array of previously unheard sounds from scratch, whether to simulate acoustic instruments or to create their own distinctly electronic sonic palette.That same year, Mr. Deutsch wrote “Jazz Images, a Worksong and Blues,” the first composition for the Moog. Soon he was giving pioneering performances at Town Hall and the Museum of Modern Art in New York.In 1968, Wendy Carlos released “Switched-On Bach,” a watershed moment for the Moog, launching Baroque musical into the Apollo age and the Moog into the bedrooms and dorm rooms of baby boomers. Ms. Carlos also used the Moog to conjure the foreboding sound of a dystopian future on the soundtrack to Stanley Kubrick’s 1971 film, “A Clockwork Orange.”After his work with Mr. Moog, Mr. Deutsch turned his attention back to teaching at Hofstra. In 1976, he published his first of three books, “Synthesis: An Introduction to the History, Theory & Practice of Electronic Music.”But in the late 1970s, he joined the Moog Company as marketing director and consulted on new synthesizer designs.By that point, sales of the American-made Moogs had begun to slide as cheaper Japanese synthesizers from companies like Roland and Yamaha came to dominate the market.In addition to his wife, Mr. Deutsch is survived by two children, Lisbeth Mitchell and Edmund Deutsch, from his marriage to Margaret Deutsch, who died in 1996; three stepchildren, Cheryl Sterling, Adam Blau and Daniel Rogge; nine grandchildren; and two great-grandchildren.The Moog synthesizer enjoyed a renaissance beginning in the 1990s, thanks to bands like the Beastie Boys, Wilco and Portishead. But by then, Mr. Deutsch had moved on from his days helping design synthesizers. He was, after all, a musician at heart, not an inventor.“A year ago I texted him to discuss something, and he said, ‘I can’t talk tonight because I have band practice,’” Ms. Moog-Koussa said. “He was 89 years old.” More