Which Halo game introduced the Forge level-editor mode?

Halo 3 introduced the Forge level-editor mode to the Halo series.

Forge first appeared in Halo 3, released for Xbox 360 in 2007. Rather than functioning as a conventional full map editor, it gave players tools to place, move and modify objects on supported multiplayer maps. Players could create custom combat scenarios, race courses and unusual game variants.

The original Forge used a floating monitor-like editing perspective and included object budgets that limited how much could be added to a map. It also allowed players to switch between editing and ordinary Spartan gameplay, making experimentation accessible without requiring separate development software.

Later games expanded the system considerably. Halo: Reach added more advanced object manipulation, while Halo 5: Guardians and Halo Infinite provided broader creation tools. Forge is sometimes confused with Halo 3’s Theater mode, but Theater records and replays gameplay; it does not edit multiplayer environments.