Well no wonder it's so hard to find. From what I can tell, it doesn't really have a name -- it's referred to variously as "The Villain's Theme" and "Enter The Villian", but even those are pretty vague in searches.

It seems that it comes from (a) silent film score(s) and appears to have no credited writer and in the public domain. Best I could glean from Google.

Here: [Link: amazon.com]
and here (iTunes direct link): [Link: itunes.apple.com]