Mine's actually a user name that had two different regeneration's (Yes, my username is now a Time Lord :P).

Basically it started during the summer before I started High School (Note, I'm now 20 in my 2nd year of college) where I joined a site called Star Wars Combine.
It's basically an open world, browser based Star Wars Galaxy you make a character and roleplay in. The mechanics were really rough at the time though so I wasn't sure how long I'd stay for so I just used a random name generator and ended up with Duvnar Magnum.

About 2 years later, Duvnar Magnum became my first and longest used forum RP character (Whose stayed to one personality type. I've technically been Gwazi longer as a character on the Guild. But he's character has already changed with each RP. Duvnar was always consistent). It got to the point where I decided it would be cool if Duvnar adopted a son to aid him on his travels. This son became Gwazi Magnum.

Then about a year after that was when the star wars community I was with introduced me to the Guild. By this point Gwazi had started to become my main character used so I made my username for the Guild Gwazi Magnum. And that became the name I used right up until the Guild crashed.

Some time before the Guild crashed though, I was playing an MMO called Guild Wars 2 with some friends of mine and my current character on the MMO was Gwazi Magnum. One time during this I got bored while waiting in the human capital, so I stripped all my characters clothes off other than pink pants and started dancing in the player lobby. :P

Within 5 minutes everyone else there had joined in and one of the friends I played with coined me the nickname Magic Magnum in reference to the male stripper Magic Mike.
I took a big liking to that name and it became a long running joke. Once the Guild was back up though and we had the chance to pick new names I figured I might as well change my name to Magic Magnum.

TLDR: Duvnar Magnum (RP Character) -> Gwazi Magnum (Duvnar's Son) -> Magic Magnum (MMO incident).

As for the Avatar?

That's just me on Christmas Day showing off all the stuff I got for Christmas including:

-N7 Hoodie
-Tom Baker's Hat
-Tom Baker's Scarf
-IT Crowd Shirt
-Breaking Bad mug
-Matt Smith's sonic screwdriver