As a teenager I was briefly obsessed with various bands, particularly those associated with the "Madchester" scene in the early 90s. One copy of the NME, which I used to decimate for pictures to stick on my school folders and bedroom walls, had a picture of Tim Booth, lead singer of the late lamented james, with the caption "Folk devil".
For no discernible reason, this has always stuck in my head, and when I was thinking up possible nicks, folkdevil seemed sufficiently /me/ and unusual to be original. I am into folk groups such as the Levellers and so it seemed to fit. The logo I designed is inspired by the Levs' Jeremy Cunningham's album artwork woodcuts. I discovered that folkdevil.com (a site by Matt Hardisty) exists - which I hadn't expected...
In media studies jargon, a folk devil is the object of widespread public moral panic, a scapegoat. Google or Wikipedia will tell you more.