Composer-arranger Sid Ramin, a longtime associate of Leonard Bernstein who won an Oscar, an Emmy and a Grammy for his work in film, TV and theater, died of natural causes Monday (July 1) at his home in New York City. He was 100.

Ramin won a 1961 Academy Award for adapting the music of “West Side Story,” which he had originally orchestrated for composer Leonard Bernstein on Broadway in 1957 (with fellow arranger Irwin Kostal). He won a 1961 Grammy for the “West Side Story” soundtrack album, and a 1983 Daytime Emmy for music for TV’s “All My Children.”

Ramin’s musical career encompassed every aspect of show business. He started in the early days of live television, arranging for Milton Berle’s “Texaco Star Theatre” from 1948 to 1956. “There was no second take,” Ramin once reminisced about the insane pace of live TV. “What you did was on the air, good or bad.”

He began working on Broadway with Bernstein’s “Wonderful Town” in 1953, although it was a happy coincidence when the composer discovered that Ramin was on the project. The two had been childhood friends in Boston — “he thrived on explaining things to me, and I just devoured every word,” Ramin said. “Lenny instilled a love of music in me.”

Bernstein insisted upon Ramin as orchestrator when he and Stephen Sondheim wrote “West Side Story” in 1957. The always-busy Ramin recruited Kostal, who was then working on TV’s other hit variety show, “Your Show of Shows,” and the two orchestrated both Broadway and film versions of the Bernstein-Stephen Sondheim musical. Bernstein and Ramin remained close friends for the rest of their lives.

“West Side Story” launched a second career for Ramin, doing theater orchestrations for more than a dozen musicals including the Jule Styne-Sondheim show “Gypsy” in 1959, Cy Coleman’s “Wildcat” in 1960, Sondheim’s “A Funny Thing Happened on the Way to the Forum” in 1962 and Bernstein and Alan Jay Lerner’s ill-fated “1600 Pennsylvania Avenue” in 1976.

Shuttling back and forth between Broadway and Hollywood, Ramin composed the iconic theme for “The Patty Duke Show” in 1963 and the theme for Peter Falk’s first TV series “The Trials of O’Brien” in 1965. His film scores included “Too Many Thieves” in 1966, the Alex Cord crime drama “Stiletto” in 1969 and a TV-movie remake of “Miracle on 34th Street” in 1973.

Ramin’s primary occupation in the 1960s and ’70s was writing and arranging commercial jingles. His “Come Alive (You’re in the Pepsi Generation)” was immensely popular, and his Diet Pepsi song “Music to Watch Girls By” was even a chart hit, reaching no. 15 in early 1967 in a version by the Bob Crewe Generation. Andy Williams had a top-40 vocal hit with it, and Al Hirt was among the estimated 150 artists who eventually recorded it.

Ramin composed or arranged some of the most famous spots in advertising history from Hertz (“Hertz puts you in the driver’s seat”) to TWA, General Motors and British Airways. For Revlon’s Charlie perfume in the 1970s, he supervised recording sessions by Bobby Short and Mel Torme.

“I get a thrill out of composing my own music, even if it’s only for a 20-second spot,” Ramin told Newsweek in 1967. “I have the freedom to express myself.” He ultimately received 12 Clio Awards, the ad industry’s top honor, for his music.

The often-performed “Symphonic Dances From West Side Story” is one of a number of large-scale works orchestrated by Ramin for symphony orchestras. He also arranged an orchestral suite from Bernstein’s opera “A Quiet Place” and, for the Boston Pops and the Hollywood Bowl Orchestra, tributes to Bernstein, Jerome Kern, Fred Astaire, Hoagy Carmichael, Victor Young and others.

Ramin recorded five instrumental albums for RCA Victor in the 1950s and ’60s and arranged and conducted albums for numerous artists including Barbra Streisand, Andy Williams, Robert Goulet, the Ames Brothers and others.

He was born Jan. 22, 1919, in Boston, the son of an advertising man who also played the violin. He attended Boston University, the New England Conservatory and Columbia University. It was while serving in the Army during World War II that he began arranging and conducting bands, which led to similar work after the war, notably for the pop group The Three Suns and trumpeter Roy Eldridge.

In 1999, Ramin received the American Society of Music Arrangers and Composers’ Irwin Kostal Award (named for his friend and colleague) “for consistent achievement in arranging, orchestration and composition for all media.”

He is survived by his wife of 70 years, Gloria; son Ron, also a composer; daughter-in-law Cathryn, an author; and grandsons Avery and Oliver. A memorial service is scheduled for 12:30 p.m. Monday, July 8, at Riverside Memorial Chapel in New York City.