I was originally looking for a username that was unique enough to not have numbers, and also had some kind of meaning so I could remember it. At the time I was lamenting that I suffer from male pattern obliviousness (inability to notice relationship cues in my own relationships, even though I could spot them in other peoples relationships) Now some form of male or guy and oblivious or obliviousness is a standard online name for me.
The oblivion rune from elder scrolls was just the first acceptable image I came across that fit when I did some googling for an avatar.