A secondary posting identity of a regular poster on an internet message board. A poster may develop several different doppels using different email addresses in order to troll and make comments that he wouldn't make when using his primary username.
Origin: The Motley Fool Discussion Boards
JoeBob has 438 doppels. Some examples: JoeShmoe, JimBob, JoseRoberto, JimeRoberto, SaddamHater, FatMan15, PoopyHead, etc.