There was only one problem: Horner hadn't written any of it down.
"I must have gotten three dozen calls. My agent got calls. They thought I was playing a game," Horner recalled in a 1998 interview for a behind-the-scenes video about the film. "But there was no printed music at all," he added. "It sounds crazy but to get that kind of freedom and fluidity in the music you can't do it writing all the notes down."
That brand of maverick unorthodoxy characterized Horner's career, which over nearly four decades provided the musical accompaniment — and the emotional beats — to some of the most memorable works of modern cinema.
The Oscar-winning composer died Monday when his single-engine S312 Tucano turboprop plane crashed in Los Padres National Forest, near the border of Ventura and Santa Barbara counties.
"Our thoughts and prayers are with James' family at this difficult time, and also with the millions of people around the world who loved his music," Horner's agents, Michael Gorfaine and Samuel Schwartz, said in a statement late Tuesday.
"We express our love and sincere condolences to James' wife, Sara, and his two daughters, Emily and Becky. And we take comfort in the belief that in his last moments, James was doing something from which he derived such great joy," the statement said.
The single-engine craft was one of several planes registered to the 61-year-old film composer, who was a flying enthusiast. The Federal Aviation Administration and the National Transportation Safety Board will investigate the crash.
While working on more than 100 movies, Horner earned six Grammy Awards and 10 Academy Award nominations, winning two Oscars for "Titanic." Horner's music undergirds the soaring battles of "Star Trek II: The Wrath of Khan" and "Braveheart," the elder-age melancholia of "Cocoon," the paternal nostalgia of "Field of Dreams" and the Space Age triumphalism of "Apollo 13."
""Khan. 48 Hrs. Something Wicked. Cocoon. Aliens. American Tail. Willow. Field of Dreams. Glory," novelist and screenwriter Seth Grahame-Smith said on Twitter. "James Horner helped score my childhood."
Born to Austrian Jewish parents in Los Angeles on Aug. 14, 1953, Horner began playing piano at the age of 5. After moving to England, he studied at London's Royal College of Music. Horner initially planned on a career in music academia until, in the 1970s, he agreed to write the score for an American Film Institute student film and instantly fell in love with the form.
"It was like lightning," he told The Times in 1995. "To me it was no different than Haydn being kept as a court composer, being paid, having the piece performed and given an orchestra."
He is best known, perhaps, for composing the music for James Cameron's "Titanic," including co-writing the penny whistle-flavored megahit "My Heart Will Go On" sung by Celine Dion.
Indeed, it is his collaborations with the extraordinarily popular Cameron — Horner also scored "Avatar" and "Aliens" — that not only earned Horner his Oscars but gave him his largest audience. The "Titanic" orchestral soundtrack sold more than 27 million copies, while "My Heart Will Go On" became a pop culture staple and one of the bestselling singles of all time.
Cameron said in an interview Tuesday that Horner's success is partly attributable to his understanding of the material.
"He got inside the movie. He really understood the film and brought to the film what it required musically," the director said. " 'House of Sand and Fog' doesn't sound anything like 'Glory' or 'Braveheart.' "
Horner seemed at times able to span these styles in short succession, maintaining a feverish work pace. In 1995, for instance, Horner had five movies hit theaters — "Braveheart," "Casper," "Balto," "Jumanji" and "Apollo 13."
But despite his many mainstream Hollywood movies, the composer had found success by drawing from unexpected influences.
The Scottish epic "Braveheart" features not only elements of Celtic music but also Japanese and Tibetan drums, part of what Horner described as an effort to create an Impressionist painting.
To fashion a fitting soundscape for the extraterrestrial setting of "Avatar," Horner worked with ethnomusicologist Wanda Bryant and employed a blend of indigenous instruments and odd vocalizations.
And in "Field of Dreams," Horner took an unconventional approach that had him flying in a couple of panpipe players from England to perform a key piece of the wistful score. It came at a significant cost — and caused executives to aim a small panic at director Phil Alden Robinson — but Horner believed the musicians were the only ones who could effectively pull off the notes.
"I think people hire me for the slightly weird angle that I bring," Horner told The Times in 1995. "Part of the trick is keeping it sort of simple; you have to give the impression of not that much music playing when there's really a lot."
Still, his myriad influences haven't always sat well with the music community. Some critics over the years have taken Horner to task for recycling the work of famous classical composers. A New Yorker piece shortly after the release of "Titanic" was particularly hard-hitting.
One of the projects Horner was recently working on was the upcoming National Geographic documentary "Living in the Age of Airplanes," a look at the history of flying narrated by fellow aviation enthusiast Harrison Ford, who survived a solo plane crash in Los Angeles in March.
Among Horner's other recent projects was "The 33," a survival drama about the 2010 Chilean miner rescue that will hit theaters in November, and "Southpaw," a boxing drama staring Jake Gyllenhaal that opens in July.
In a statement to The Times on Tuesday, that film's director, Antoine Fuqua, described a composer who took a wholesale approach to his craft.
"James was not only a composer. He was a true filmmaker. He cared about the music, but also about the story as a whole," Fuqua said.
Horner described that skill as requiring, at times, two competing impulses — a need for control and a more improvisational sensibility.
"You have to be right on top of it so that you know how it's all going to work out," he said of his approach to scoring in the "Field of Dreams" video. "But you have to be fluid enough that things will change."
Oliver Gettell, Matthew Hamilton and Rebecca Keegan contributed to this report.