R is for Ragnarök
The twilight of the gods in Scandinavian mythology, when Odin, Thor, Freyr, Loki and Týr meet their final end.
I think there's something rather glorious and terrible about a world-view in which just about everyone is doomed to die in one final cataclysmic battle. Although, after the battle, you'll be pleased to know, there are a few survivors and a peaceful new world dawns. So that's nice.
The word is derived from ragna, the gods or the ruling powers and rök, meaning fate or an ending.
Archaeopteryx Blunderbuss Chthonic Dreadnought Entropy Fulgurite Gargantua Humbucking Ichthyic Juggernaut Kappa Labyrinthine Megrim Numinous Ophidian Pandemonium Quark Ragnarök