We have spent three essays in this booth arguing about a chant. We watched Neil Davidge throw it out in Halo 4, Kazuma Jinnouchi bring it home in Halo 5, and a trio of fans rebuild it for good in Halo Infinite. But every one of those arguments was really about something that already existed, a sound so complete and so beloved that touching it at all felt like sacrilege. This is the story of how that sound was made.

It begins in July 1999, in a car, with a man humming to himself like a monk. Bungie's director of cinematics, Joseph Staten, had walked over to audio director Martin O'Donnell with a near-impossible ask: a piece of music for the upcoming Macworld demo of a strange new game called Halo, and he needed it in days. Staten wanted something that felt ancient, epic and mysterious. O'Donnell, drawing on a fascination with the music of the Middle Ages, came up with the idea of opening the piece with Gregorian chant, and he jotted the melody down while driving. The theme was written in three days. The franchise would spend the next two decades trying to live up to those seventy-two hours.

▸ Release File

Halo, Halo 2 & Halo 3 — Original Soundtracks

Composed by Martin O'Donnell & Michael Salvatori · Bungie / Microsoft, 2001–2007. Three games that built the most recognisable sound in video games, from a three-day chant to a sixty-piece orchestra.

The brief: ancient, epic, mysterious

The deadline was brutal. O'Donnell was asked on a Thursday for music that would have to be recorded and shown internally the following Monday, the same day Bungie's people flew to New York, before debuting at Macworld on the Tuesday. From a handful of words, ancient and epic and mysterious, he built the most famous thirty seconds in the medium. The opening was Gregorian chant, sung not by a hired choir but by O'Donnell, Salvatori and three jingle singers the pair had worked with on commercials. Over the top came a wailing, Qawwali-flavoured vocal solo. O'Donnell had meant for one of the professionals to sing it, but after he demonstrated what he wanted, everyone agreed he should do it himself.

The bones were stranger than they sound. O'Donnell has said the four-phrase structure of the chant was lifted from the opening of The Beatles' Yesterday, and he described his own taste as "a little Samuel Barber meets Giorgio Moroder", classical weight crossed with electronic pulse. Because he had no idea how long the Macworld presentation would run, he built deliberately loose opening and closing sections that could be stretched or trimmed around a driving rhythmic middle. That improvised flexibility, music designed to expand and contract on demand, turned out to be the seed of everything the franchise's scores would later become.

The partnership

O'Donnell did not build the sound alone, and it matters that he never pretended otherwise. He and Michael Salvatori were partners in a freelance company called TotalAudio, veterans of jingles and earlier Bungie games like Myth and Oni, and they composed every Halo score together. When Microsoft bought Bungie, O'Donnell had joined the staff barely ten days earlier and moved to Seattle, while Salvatori stayed in Chicago to keep TotalAudio running. The two worked the distance by sending music back and forth for feedback, a long-distance collaboration that produced the most unified sound in the medium.

There is a piece of luck buried in the origin story, too. A fire had burned down their studio in 1999, and rather than simply rebuild, the pair used the insurance to upgrade to newer equipment, which let them produce Combat Evolved in 5.1 surround sound using digital, hard-disk recording rather than tape. Live players from the Chicago Symphony and the Chicago Lyric Opera Orchestra were layered over MIDI and sampled instruments, reverb and overdubbed cellos faking the scale of a full orchestra. The famous Halo sound, in other words, was half ancient liturgy and half clever studio illusion, built by two friends a couple of thousand kilometres apart.

Combat Evolved: the liturgy is set

When Halo: Combat Evolved launched the Xbox in 2001, the theme that began the whole thing became the spine of an entire soundtrack. O'Donnell and Salvatori threaded the chant, the string melody and the Qawwali colour through cue after cue, so that the music felt like one continuous body rather than a collection of tracks. O'Donnell had a name for the principle: emotional equity. He liked to cite his teacher's mentor, the film composer Alfred Newman, who held that good themes should be reused relentlessly, because a bad theme would never have been used in the first place. That single idea, repeat the good melody until it means something, is the genetic code every later Halo composer would inherit.

The other revolution was invisible and enormous. Working hand in glove with the level designers, O'Donnell chopped the music into "chunks" that the game's audio engine could reassemble on the fly, swelling for a firefight, dropping to silence when the tension demanded it, stretching to fill however long a player loitered in a space. Interactive, non-linear scoring of that kind was rare in 2001 and is everywhere now. The soundtrack almost never reached the public at all: Microsoft saw no reason to release it, and only relented after sustained pressure from O'Donnell and a nudge from the producer Nile Rodgers. When it finally arrived in 2002 it sold tens of thousands of copies to people who had never needed the game to love the music.

▸ Installation 04, the alien wilderness where the first score had to move between quiet exploration, sudden firefights and the vastness of the ring itself.

Halo 2: the guitars

If Combat Evolved was monastic, Halo 2 plugged in and turned up. For the 2004 sequel, O'Donnell brought in heavy electric guitar, most famously from the virtuoso Steve Vai, and the result opens the soundtrack as the Halo Theme Mjolnir Mix, a roaring rock reworking of the choral original that is, to a lot of fans, the single most iconic track the series ever produced. Producer Nile Rodgers, the Chic legend, oversaw both volumes, and the studio footage of Vai shredding while Rodgers conducted him by mouthing guitar lines and O'Donnell watched in disbelief has become a small piece of gaming history in its own right.

The release was as ambitious as the music. Halo 2 shipped its soundtrack in two volumes almost two years apart. Volume 1, timed to the game's launch, mixed O'Donnell and Salvatori's arrangements with "inspired-by" rock from Incubus, Breaking Benjamin and Hoobastank, while Volume 2, in 2006, gathered the actual in-game score into long suites and was, for many, the album fans had really been waiting for. The orchestral parts were tracked with the Northwest Sinfonia at Studio X in Seattle. Volume 1 became the first video game soundtrack ever to enter the Billboard 200, peaking at number 162, a milestone that helped drag game music toward being treated as a serious art form rather than a novelty.

Halo 3: blowing it out

For the 2007 finale, O'Donnell wanted to "blow out" the epic sounds the series had only ever hinted at. Where Combat Evolved had faked an orchestra, Halo 3 hired a real one: a sixty-piece orchestra and a twenty-four-voice choir, with C Paul Johnson joining O'Donnell and Salvatori, and the music recorded live rather than synthesised. The album abandoned the suite format of Halo 2 and returned to the level-by-level structure of the first game, and it leaned harder on previous motifs than anything before it, because O'Donnell believed a trilogy capper had to be built from the audience's own memories.

Two new pieces became permanent. One Final Effort gave the heroes a soaring brass anthem that has been reprised in every era since. And Never Forget, a reworking of Halo 2's aching Unforgotten, distilled the whole saga into a few downcast piano notes, the cue Jinnouchi would later reach back and reinterpret in Halo 4. That piano voice was itself a Halo 3 innovation; O'Donnell, who always composed from the keyboard, introduced the now-beloved piano theme in the game's announcement teaser. The closing cue, fittingly, was called Finish the Fight, folding the Halo theme and older melodies into one last triumphant blast.

The themes that continued

Trace the throughline and the genius of the Bungie years is obvious. The Halo theme itself mutates across all three games while staying instantly recognisable: synthesised and monastic in Combat Evolved, given electric teeth as the Mjolnir Mix in Halo 2, then re-recorded with a live orchestra for Halo 3. The mournful Unforgotten from the second game becomes Never Forget in the third. The piano theme arrives late and instantly feels eternal. This is emotional equity in action, the same melodies returning in new clothes until familiarity itself becomes the feeling.

What O'Donnell mostly avoided was strict, character-by-character leitmotif. Rather than assign a tune to each person in what he jokingly called a "Peter and the Wolf" approach, he wrote sad music for sad moments and scary music for scary ones, letting recurring themes emerge by feel rather than system. It is a looser, more atmospheric philosophy than the cinematic leitmotif scoring the later composers would lean into, and it is a large part of why the Bungie scores feel less like film music and more like the weather of a place.

The end of an era

The pair kept stretching the sound after the trilogy. Halo 3: ODST abandoned the established themes almost entirely for a smoky, jazz-noir mood to suit its smaller detective story, and Halo: Reach, a prequel to Combat Evolved, went grittier and darker to match a tale of doomed soldiers. O'Donnell called the chance to write genuinely new music both a challenge and a relief from the weight of the iconic themes. Reach was Bungie's last Halo. After the studio split from Microsoft to make Destiny, O'Donnell was fired in April 2014, an unhappy end for the man who had given the franchise its voice.

The affection, though, never dimmed. Bungie buried tributes to him in the games themselves, a recurring tune called the Siege of Madrigal that has hidden in Halo soundtracks since Combat Evolved, and a marine in Reach named M.O. Donnell with the service tag MRTY. In 2015 the music of Halo was voted into the Classic FM Hall of Fame, the first video game music ever to make it, a quiet confirmation that what those two men built in a Chicago studio had become part of the wider canon of music, full stop.

The inheritance

Everything we wrote about in the modern trilogy only makes sense against this foundation. When Neil Davidge threw out the chant for Halo 4, this is the liturgy he was refusing to recite. When Kazuma Jinnouchi reached back to restore it for Halo 5, these are the themes he was reaching for. And when the three composers of Halo Infinite rebuilt the original sound for good, this is the home they were moving back into. None of those choices would mean anything without the thing O'Donnell and Salvatori made first.

That is the strange power of a great theme. It outlives its authors' tenure, survives departures and homecomings and committees, and keeps meaning more each time it returns. The whole saga of the Halo score, the departure, the restoration, the long way home, is just the sound of a franchise circling back, again and again, to a melody one man hummed to himself at the wheel of a car because a colleague needed something ancient by Tuesday.

It started with monks in a car, three days before a deadline. Everything after — the guitars, the grief, the departures, the homecomings, the long way back — was just the franchise spending a quarter of a century learning what that one melody already knew.