Ripplin said:

I just heard this 'rule of two' thing on MADtv on Saturday. I still don't know what it means, really. Can anyone supply a good link to explain it? (or just do it themselves if they have a minute)

Yoda in TPM says "Always two there are, no more, no less. A master, and an apprentice." The EU story goes that there were once thousands of Sith until they all tried to kill each other, nearly driving them to extinction. The only Sith left (I'm trying to do this without looking up anything, so I don't know his name) took one apprentice, and it pretty much became a rule from then on that there would only be two so they wouldn't be too tempted to just wipe each other out. It's assumed that if the apprentice was taking an apprentice, then the master was on his way out. The problem is that according to the EU, Vader had at least two apprentices and was actively searching for Luke to be his next and Palpatine had at least two others also. Maybe they were going to repopulate the Sith after 2000 years.

Or the EU isn't worth it anymore.