Hmm, I've only had 2-3 usernames, and then I've used them for everything. When I was younger I used to go by Wyvern, a word I picked up from Monster Hunter, which I became pretty obsessed with at the time. With that I played for a couple of years, until I wanted a change ('I'm a big boy now!' was probably a motivator. That, and I was jealous that people had more original usernames)
I think I picked up Wazulu in a music lesson quite a few years ago, when we had to learn about African dance. I use it for its originality (I believe there are only 2-3 others who use it to a large scale) and its sheer adaptability.