My Avatar is my elite model on Halo 3 multiplayer, and if Halo Reach so allows it I may replace this with my elite picture in that games multiplayer as well.... same colors of course.
The point is, I've always been an aqua elite in Halo multiplayer games hence it's evolution is an evolution of my gaming history as a whole.
As for my name, well I once mispelled 'Trex' on a Halo 1 profile name, liked the mispell and kept it. Then later I moved from Xbox to Xbox360 so the name changed.