My online nick started out as the "field-name" of a character (who is a modern-day ninja-trained professional assassin, potentially immortal) I made
for the GURPS role-playing game over 15 years ago. Originally, the field-name used was simply Midnight.
However, once I decided to use it for myself online, I found a lot of Midnight names as well as a lot of variations of Midnight already being used
(Midnight Defender & Midnight Madness being a couple of them, as well as our own Midnight Multilator

). So I had to come up with a different
variation: Midnight Destroyer.
However, when I tried to use the full name, many places that I went to that required a login ID, they didn't provide enough room for that many
alphanumeric characters...So I shortened the name to what you now see. If I need to shorten my nick even more, I usually vary the spelling of Midnight
(as MidniteDStroyer, MidnytDStroyer, etc) or just tack a 12 or 1200 on the end of Midnight (ie:Midnight12 or Midnight1200).
My avatar is a pic I drew of my GURPS character wearing his full field-outfit...What you see of that pic is a head-n-shoulder cropshot from the
full-figure drawing.