From the experts:
An fearsome old Norse name with a long history in Scandinavia. It's gotten a boost in the States from popularity of the History Channel drama "Vikings," in which the protagonist is named Ragnar. Ragnar Lodbrok (meaning "shaggy pants") was a legendary warrior whose story was told in the Viking sagas. Ragnar also recalls name of the Norse Judgment Day, Ragnarök.
Easier versions here would be Raynor or Rainier, as in the late prince of Monaco.