It's my high school nickname. My real name is Adam, and one day at a debate tournament I drew charicatures (sp?) of everybody on the team.
I don't draw well, mind you, but it was just to poke fun at everybody (everybody took it well, tarry not). I drew myself as "Don Adam Martin, Mafia Crime Lord and the Sexiest Man Alive."
Suffice to say, it stuck. I was henceforth either known as "Don" or "The Don" to everybody. The teacher (Mr. Dennis, aka Poppa D) and a few others used "The Don" so profusely that they even used it in the vocative, as in "Hey, The Don, come check this out."
The nick name quickly exploded into a full fledged mythology about the Don's family. I, the quintessential nerd and anti-socialite, managed to become the center of social existence among the debaters from several schools, simply by arbitrating who was in the family and who were The Don's People (I always take care of my people).
I've known people for months without them knowing that my real name was Adam and not Don, since so many people called me that, and I still answer to "Don" instinctively.