It started out as WishfulNemo. I always liked the meaning of 'nemo', the thought of being a no one on the internet appealed. I attached a 'Wishful' in front of it as a wink towards the meaning of my real name.
Later I changed it to Nemopedia, because everyone started to call me Nemo and I'm a know-it-all. It was a joke, but I liked it enough to have it as my username. XD