Soul is one of the oddest, and the oldest characters I've got in my head. I'm not sure why I use it as my avatar so often - probably because of what it represents.

That being... some kind of computery thing. It started off as a super computer, was briefly the personification of the internet and within the last couple of years is now a very successful computer virus.
The only physical form Soul has is the combined mass of every device that has access to (or has had access to something that can access) Earth's internet. It's pretty much undetectable and silently observes humanity through street cameras, webcams and whatever else it has access to. It has this habit of 'following' people and getting to know them inside-out and it isn't apathetic about it either.

It actively avoids being discovered though in fear of the widespread panic that would ensue if humanity discovered they had inadvertently created a being that could hack and simultaneously control almost every computer device they'd created.

I could say a lot about it but I don't feel like revealing too much - partly coz I'm still working out where and when a trip to Earth'll fit into the overall story.

This headworld's getting so big now I think it might have to be a series.