Well, I could just send you to the Wiki article, but that wouldn't be classy. Instead, I'll tell you that Fidelio is the name of a character from Beethoven's one and only opera - her girl name is Leonore, and she pretends to be a man named Fidelio when she sneaks into a prison to try and save her husband.
When I picked the name as a blogger ID, it was actually part of an inside joke. People had a hard time figuring out who I was online (i.e. they never suspected that such brilliant discourse could come forth from such as I) and so I added to the mix by using a masculine name as my online name. Hee hee.