Are you sure you want to know? Wouldn't it be more fun to guess? You could hypothesize or years without getting it right.
The "D" stands for "Daingerfield", which was my mother's maiden name. It's a custom in parts of the Southern United States to give girls their mother's maiden name as a middle name (and it's treated as a 2-element stack; if you change your name when you marry, you lose your original middle name and treat your maiden name as your middle name). No, it is not Rodney Dangerfield's real name.
I was stunned to do a Web search and find 802 pages about Daingerfields. Mostly they're about Daingerfield, Texas, which I had never heard of before. Then again I hadn't run into Daingerfield Island in Virginia (but the fact that its story involves a Bathurst Daingerfield strongly suggests that these are relatives of mine; a fondness for obscure first names is characteristic), or the artist Elliott Daingerfield There's also a Daingerfield Road in Alexandria that's good for a large number of accidental hits, and a genealogy site with somebody else with Daingerfield as a middle name. I was happy to find a quote from my grandfather, and startled to discover a character in Faulkner.
Because I like "EDZ" better than "EZ" as initials.