In the beginning, there was The Gallery. No, hang on; that’s later.
In the beginning, there was a bunch of people who knew each other and liked hacking on things. Or maybe it goes back earlier than that, before we all met? Who knows - in the beginning, there was Cambridge University, and some time after that we all arrived and started getting to know each other.
The Gallery was an experiment to discover if some of us could bear to live together; it went pretty well for several years, until people started getting married, buying houses and so forth. We got a domain for it, since every real geek house clearly needs its own website.
Then James Aylett bought the domain tartarus.org on the basis of its being cool and fitting in nicely with his habit of naming computers after damned and tortured souls. It seemed only natural to use it to hold information about the various things we do, and besides gives us the chance to create silly email addresses for ourselves.