Who composed most of Portal 2's original music?

Mike Morasky composed most of Portal 2’s original music.

Morasky was Valve’s lead composer for the game’s backing score, creating electronic, synthesized, and procedural music designed to react to the player’s actions. His approach matched Aperture Science’s deliberately mechanical atmosphere, using arpeggios, unusual rhythms, and sounds intended to feel as though they were generated by a computer.

Portal 2 also includes important musical contributions from outside Morasky’s score. Jonathan Coulton wrote “Want You Gone,” the end-credits song performed by GLaDOS, while the band The National contributed “Exile/Vilify.” Those songs can make the soundtrack credits seem more divided than they are.

Kelly Bailey composed music for the original Portal alongside Morasky, but he was not the principal composer of Portal 2. Gabe Newell was Valve’s co-founder and executive, not the game’s composer.