Bungie developed Halo: Combat Evolved for its original Xbox release.
The game began as a project at Bungie, the Chicago-based studio previously known for the Marathon series and Myth. Microsoft acquired Bungie in 2000, helping position Halo as the flagship launch title for the Xbox. Bungie handled the game's design, programming, art, and audio production.
Halo: Combat Evolved launched in North America on November 15, 2001, alongside the original Xbox. Its blend of science-fiction storytelling, vehicle combat, rechargeable shields, and console first-person shooting helped establish the Xbox brand.
A common mix-up is crediting 343 Industries, but that studio was formed later and took over primary Halo development after Bungie separated from Microsoft. Ensemble Studios developed the real-time strategy game Halo Wars, not Combat Evolved.