Ragnarok

Ragnarök is the name of the event which foretold the end of days in Norse mythology. It foretold the death of the old Norse gods including Odin, whose death was to occur at the hands of the wolf Fenris.

Season 9
A cult known as The Maw of Fenris saw Ragnarök as a plan of action to wipe out humanity, leaving only werewolves to inherit the Earth. They worshipped Fenris as a god and wanted to rule the earth. The cult was eradicated by the efforts of Reverend Jim Myers. But nknown to him, his wife Joy restarted the cult after her brother was killed by a hunter. She believed, along with her father, that as along as man lived, he would only destroy. She wanted to the werewolves to rule them and for that planned to convert the reverend to her cause. She kidnapped Garth and Bess and was going to kill them and pin their murders on the brothers. This would finally turn the werewolf community against the humans. But she was killed by Dean who put a stop to their plans.

Trivia
Ragnarök was mentioned by Odin is Hammer of the Gods, who declared that he would die when Fenris would eat him. But he was killed by Lucifer later on in the episode.