Mine began back in the days of the CB radio. You all remember CB's. That's what people like us did before there was this interweb thing.
Anyway, before I had my own radio, I was sitting with my friend who was talking on his CB. Someone on the radio asks who that is they hear in the background. My friend whispers to me "Don't use your real name." so I just said the first thing that popped into my head; "Major Mudd", which was a kids show in Boston in the 60's; which I really liked when I was a kid... living near Boston... in the 60's.
Anyway, it stayed with me when I finally got my own CB and my friend just shortened it to Mudd.
Since then, whenever I've needed an alias on the Net, I've aways used Mudd. (Not the character from the original Start Trek, as most people guess).

BTW, that's the real Major Mudd in my avatar.