Bit of a sad story to be honest.
When our family got the internet at home, my Dad, (whose nickname since high school was curl on account of his hair) signed up to IMDb. He just used his name, but apparently 5 people had beaten him to it, so he became "curl-6". For convenience, I used the same profile as him, so I was "curl-6" also.
Shortly afterwards, when I was 19, he died of a heart attack, completely out of the blue.
After his death, I continued to use the curl-6 profile on IMDb, and later when I signed up to other websites like VGChartz, I retained the username, both out of familiarity, and I guess as sort of a remembrance.