The music of the Halo series has long been considered some of the most iconic of all video game music. O'Donnell served as composer and audio director of every Halo game developed by Bungie, as well as games like Oni and the mega-hit, Destiny.
When asked about the creation of Halo's signature theme, O'Donnell revealed that it had all been composed within two days for the unveiling at MacWorld 1999. The inspiration came from a mere three words conveyed to O'Donnell by Bungie's Joe Staten: ancient, alien, epic.
After speaking with Staten, O'Donnell hummed improvised monk chants to himself while driving home. He had composed the famous monophonic Halo chant by the time he arrived. O'Donnell also composed the fanfare for The Game Awards of 2014, and has recently founded a new development studio, Highwire Games.