I've explained this already in the previous topics asking the same question ( ) but in short:

My parents wanted to name me "Geoffrey James" but they thought it sounded too much like Jesse James, so switched it to James Geoffrey. The G is in honor of my mom's mom, Grace, who died before I was born. As for the letter J, I'm not quite sure the significance, but everyone else in my immediate family has a middle name starting with J, including my parents. While my name is officially spelled Geoff, it was spelled Jeff in grade school because it was easier I guess. I later reverted back to Geoff in high school I think. In school I always had to say, "call me Jeff/Geoff" on the first day, but after a while (after high school) I didn't feel like explaining it any more, so started answering to James as well.