urbandictionary.com has a good definition as well.
Ldub came form the fact that his last name is like wijokotoajskoski.
I asked him about this either at moab or on a thread buried somewhere. His brother would go by Jdub or whatever his first initial is, I can't remember but I think it was when we took a break on Poison Spider and he scored that sweet piece of wood out in the middle of nowhere while others(Billy) scouted ahead. Not 100% sure, but there were talks about his time in Hawaii as a "kona" farmer in the same conversation...
If he were in the navy, we would call him W13 or however many letters were in his last name.