It's a lame superhero name my 8 years old self thought about 'cause "hey, my name is Matt, what would be more cool and radical than being a superhero with a 'x' in my name?". It got stuck in my head ever since.
So, while creating my first accounts around the internet some years ago I didn't really know what to use as a nickname and just rolled with it.
I would happily change it now but sadly, considered that Deviantart doesn't let you change your name unless you pay for membership, I'll probably be stuck with it for a looong time.
Trust me, I tried.
On most other sites I'm known as Komodo23, by the way.