I have been using this nickname since the Internet was unheard of, and local dialup BBS's were all there was. Invictus is latin for "unconquerable". The original inspiration came from the poem Invictus by William Ernest Henley. My favorite poem of all time. I was infuriated to the point where I beganthrowing things around my house when Timothy McVeigh (the unabomber) used that poem as his final F-YOU to the world. I was literally seeing red. But, I decided that if I change my nickname because of it, I'm letting him win.
Anyway, Invictus is also in my heritage. I'm mostly Scottish, and on my dad's site of the family, clan Armstrong, the clan motto is "Invictus Maneo" - "I remain unconquerable" or "I remain unvanquished". (It could mean either).
So there ya go.