For millions of Halo fans the series' iconic monk chant introduction music is instantly recognisable but it almost didn't happen.
According to its composer, the monk chant was originally designed to accompany the Halo tech demo shown by Apple's Steve Jobs in 1999 - and nothing else.
"We didn't have much time," Bungie composer Marty O'Donnell reminisced to IndustryGamers, "so I thought if I was going to do something epic and ancient maybe I could start with some monks chanting.
"I thought, if I just say this to them, they'll be like, 'No, this isn't right. What are you thinking? This is a first person shooter.' So instead of saying anything I just went and recorded something and then I played it for them; and it's not like they had a lot of choice but they could have said, 'Please remix this' or something.
"We had one more day to redo it. I remember playing it for Jason Jones and Joe Staten, and they seemed really relieved and really happy and then we played it for the rest of the people at Bungie and they were excited about it, so we got on the plane that afternoon and took it to New York.
"Primarily, at that moment, that piece of music was for that show. It was, 'This is what Halo feels like for that show' and it was great that in the subsequent years I was able to pull themes and moods that were started right then."
Halo's transition from a Mac and PC game to Xbox launch title to one of the biggest games ever is well documented, as is Bungie's success.
But following the developer's decision to leave Halo behind for a gargantuan 10-year publishing deal with Activision, the monk chant music, along with the IP, is in the hands on Microsoft and its in-house development studio 343 Industries.
This, for O'Donnell, is "bitter-sweet".
"Walking away from the Halo universe... I had so much music I'd created over the last decade and walking away, I go, 'Well, all right. That's the end of that. We can't even pull from that music any more for anything in the future at all. It's all for Halo.'
"So essentially I'm just taking all those CDs and - I don't know what there is, maybe 40 or 50 hours of music - and just putting it on the shelf and moving forward on to something brand new. It's kind of a relief because from a creative standpoint it's great to just have an absolutely blank sheet of paper, but then on the other hand blank sheets of paper are scary to creative people. I'm not saying I have writer's block, but we'll see..."