I love emperor but i dont think they were the kings. although they were the band that bought black metal more to the masses to an extent. I would have to say mayhem or Burzum. Its cold, its raw and its the sound of fucking winter.
Bathory should definitely be included, altho Quarthon certainly shifted genres throughout his long career. As to the "kings", (Burzum is a band of one) as much as I like Emperor, they are a tad too symphonic to my taste, at least when I think of Black Metal. Gotta go with Burzum; those first four records are absolute classics. Burzum incorporates some dark ambient passages on his early albums, but they accentuate the purely black metal tracks.
It's certainly not Emperor - one good album does not maketh a band
Burzum was superb early on but I can't go past Immortal for consistency. No other BM band has released brilliant album after brilliant album (even though technically they weren't really a BM band after the first few albums).