Real name: Not applicable
First appearance: Justice League of America I#16 (Dec. 1962)
Abilities: Mind controlling music
Worst act: Theft, kidnapping
Quote: "Certainly not! I've arranged for you to be so busy dancing--you won't be able to stop them!"
Created by: Gardner F. Fox (script), Mike Sekowsky (pencils), Bernard Sachs (inks)
An oddity here. Imaginary stories were a unique thing at DC. Basically a what if or elseworld, with the main theme being that it wasn't canon. In other words, this is just a show and you should really just relax.
So, the story here is actually credited to JLA superfan Jerry Thomas (a mash up of Jerry Bails and Roy Thomas), who on a whim writes to the JLA with a question, what if this villain I just created fought you? He plays the experiment fairly, I'll say.
The Maestro is committing a string of robberies, aided by his music which forces people listening to dance uncontrollably. Shades of the Music Meister, eh?
The JLA is actually fairly stumped for a bit when the Atom comes up with a novel solution. All in all, not bad but I'm honestly curious why this would be imaginary?