Ragnarök = the end of the world, when monsters rise up and kill the gods and destroy Miðgarð and Asgarð. Thor and the Miðgarð Serpent kill each other. Oðin is killed by Fenrir, who is then killed by Oðin’s son, Vidar. Tyr and Garm kill each other, as do Heimdall and Loki. Surt kills Freyr and sets fire to the world killing all men and gods.
Fimbulvetr = "Terrible Winter" Three winters with no summers in between which precede Ragnarök.