The Underground is Bungie's oldest official forum located on Bungie.net. It was originally for discussing anything related to Bungie.
On July 26th, 2002 The Underground was launched as Bungie's main, first, and most popular forum for fans to frequent. It along with The Septagon became the only two forum's Bungie sponsored on their homepage, Bungie.net at this time. The Underground was styled the same way Chapters forum's were with topics being able to created in sequential order with the absence of "bumping." Replies cascaded downward and were viewable upon clicking the corresponding link.
On June 24th, 2004 bungie.net was significantly revamped and The Underground was remade as such to operate with the new website. The forum name was slightly changed to Bungie General: The Underground. It's purpose however changed from being just general discussion about Bungie and everything related to being more specific in anticipation to the massive influx of new members because of Halo 2's upcoming release. It's new designation was for Bungie general discussion and oldschool games predating Halo. Its form changed drastically as well with no cascading replies, but included members join date, and briefly a post counter.
Second New Hawtness
The Underground didn't change much in the wake of the bungie.net's fifth major overhaul initially in regard to the fundamental rules and guidelines of the conduct on the message board. The look did change however but didn't deviate from the basic format that was commonly seen throughout its existence. But in the grand scheme of things it would be nothing compared to what the Bungie Community Team had in mind for its future...
The Bungie Universe Forum
On June 1st, 2009, The Underground dissapeared and The Bungie Universe Forum took the place of its original forum ID and completely changed not only the name but the look, feel, purpose, and rules. The Bungie Universe Forum became for discussion of all elements of the storyline, backstory, plotline, and canon elements of all Bungie games, including Halo, Marathon, Oni, Myth, and others. Additionally, this forum is for discussion about World Domination, Bungie LLC itself, Bungie lore, and future projects.