Back in the early- to mid-2000’s I usually had handles related to my favorite characters from some anime or fantasy novel, however, inevitably I would be embarrassed by those names as time went on and my interests shifted. So at some point, I decided to just drop these types of handles, and for a long time I simply used my first name on a few fora (Mathias). However, some years ago when I had to create a handle for the purpose of online accounts I decided that this was perhaps somehow a bit too personal after all, and prefered something slightly removed from my name.
SU2 is an important symmetry group in quantum physics and its fundamental representation is often used to designate a symmetry between two values an object can take. As my last name also starts with an M, I decided to use the handle SU2MM in order to imply symmetry between the two M’s. I thought it was kind of neat for anyone who might get it and for the vast majority of people it would simply be a relatively neutral handle.
I have yet to decide on an avatar. I used to have one of Yang Wenli from Legend of Galactic Heroes on many fora, but I guess I have become very self-conscious about utilizing characters from media as part of my online identity.