Apparently classifying something as extreme metal is more difficult than you suggest. I don't agree with King Diamond being versatile, but if you are willing to call early Mercyful Fate (heck, all of MF) Black Metal, that would to me, constitute extreme metal. On the other hand, the guy from Primordial lacks both the themes and sound to be anything remotely extreme metallish, but for some reason because his vocals are slightly 'shreikish' Primordial is suddenly extreme?
Ofcourse, none of this is really important to the thread, but there is a lack of consistency in the arguments put foward. Anyway, I still love Mercyful Fate and from what I have heard, Primordial is pretty wicked too. It seems that anything Life Sucks whacks in his sig, is worth listening too - I just got Mourningful Beloveth (I think its called .. and I'm itching to listen to it in full.)
Matt Chalk seems to be the favourite in this thread - Sceptre of the Ancients rules \m/