Mine goes back to my teenage years, got the nickname Feral after a fight broke out and I waded in to stop people getting hurt. So just to be different I added an extra r and that's that.
When I first joined 2003 I was named Grendel which is a name I used on Tweakers Asylum prior to HEXUS and it rolled over from that and was taken from the old story Beowulf at the time as I was into all things Anglo Saxon.
On PSN & XBox I am known as Grimmsqueaker which isn't a typo given all the variations of Reaper and Grim Reaper etc. Fans of Terry Pratchett know it is the Death of Rats which always makes me chuckle and I started using it as my nickname when I joined PSN 2009 with my PS3