Carmela Ciuraru has a small photo-essay in the Huffington post about writers and their pseudonyms -- and the reasons behind the pseudonyms. Her tone is a little snarky for my taste, but the mini-biographies are interesting.
Perhaps the first character we invent, as writers, is ourselves.
"EM Lewis" isn't really a nom d'plume -- it's just my initials and last name. And I didn't decide to use it to hide my gender, or because I am a convicted felon (as one of Ciuraru's writers did). But I do like having my own alternate self. Somewhere between me and her and all of my characters lies the real me.
And... that's enough psychoanalysis for now.