One of the most common things I hear from people when they read my Gundam Wing/Xenogears crossover 'The Longest Dream' is:
Well, I used to use a link to the Gaming Intelligence Agency (may they rest in peace) that had all the info on Xenogears anyone would ever need. Their website folded, however--so I snagged all the info I could off of their site (Like they said we could, so nyah!), combined it with some images and artbook scans of my own, and decided to put up my own little Xenogears archive.
In courtesy to the original author(s), whoever they might be, I'd like to emphasize that I did not write these summaries or character biographies. (In fact, if they see this page, I would love it if they e-mailed me so that I could give them proper credit and kiss their feet as an unworthy fangirl! )
Anyway, to be brief: Xenogears is a Playstation game produced by Squaresoft. It has one of the most mind-numbingly twisty plots I've ever seen. I recommend everyone play it--but if you don't want to, or don't care about being spoiled, here's all the information you'll ever need to understand the story.
Last warning--HERE BE SPOILERS!