.hack is a multi-media project. Anime, Games, Comics and Novels. All woven together to form a huge complex world and plot.

The original .hack idea was code named Project .hack while the whole of everything involving G.U. was under the name of .hack Conglomerate. They plan all of this stuff out well in advance so nothing really seems tacked on. It was a huge risk initially but it paid off big time.

Better yet...go to the dot hack wiki .hack//Wiki - .hack//Wiki - a Wikia wiki