The Halo theme first appeared in Halo: Combat Evolved, released by Bungie in 2001, with music composed by Martin O'Donnell and Michael Salvatori. Its chant-like choir and orchestral swell became the signature sound of the Xbox era and one of the most recognisable pieces of video game music ever written. As Halo grew into a cultural phenomenon, the theme spread far beyond the games into YouTube montages, memes and parody edits, where a few seconds of it signals that something epic is about to happen.