lol Caits had one right for the mythology. Didn't know about the other thing. 

But it's kind of like doomsday or the end. Like the final battle for the norse mythology. I'm pretty sure Loki had some hand in starting it. 

Also... the first gang in History's Mightiest Disciple Kenichi was called Ragnarok. 

OH YEAH!
There's also a Thor clone in marvel called Ragnarok I think lol