In Germany there are a number of legends concerned with a sleeping king or emperor who will awake to save the Vaterland at the time of its greatest need. The sleeping hero is usually Karl der Große (not a hero but a xtian butcher in my opinion), Friedrich Barbarossa or Heinrich der Vogler (the Fowler, 876-936).
Karl der Große (Charlemagne/Charles the Great) was born in either 742, 747 or 748. There is no agreement on the date but we know he died in 814. He became King of the Franks in 768, King of Italy in 774 and Emperor in the West from 800. He is remembered particularly for his wars of extermination against the heathen Saxons in the 770s and the 780s along with the destruction of the Irminsul and many other shrines and temples.
Heinrich was the founder of the Ottonian dynasty, the first emperors of the First Reich. His son Otto I became Germany's first emperor. Heinrich became Duke of Saxony in 912 and was elected as the first Saxon king of East Francia (Deutschland) in 919. East Francia was the eastern division of the Carolingian Empire and lasted from 840 until about 962. This was the foundation for the modern German state. Wagner regarded Heinrich as a suitable historical figure for the pan-German movement to rally around and featured him in his 1850 music drama, Lohengrin.
Friedrich I (Barbarossa, 1122-1190), Duke of Swabia from 1147-1152, became King of Germany in 1152 and Holy Roman Emperor of the German Nation in 1155. He became known as Barbarossa because of his red beard.
A detailed history of mediaeval Germany may be found in Benjamin Arnold's Medieval Germany 500-1300. A Political Interpretation, 1997.
Regarding Karl der Große he is said to slumber in many places, in particular in the Desenburg near Warburg, in the castle of Herstalla on the river Weser, in the Karlsburg on the river Spessart, in the Trausberg and in the Donnersberg in the Pfalz. Interestingly the Donnersberg is named after the German God of Thunder, Donar. The Romans called the mountain Mons Jovis after their Jupiter who as we know is also a deity associated with thunder and lightning. The highest point of the mountain is called the Königstuhl (King's seat) and the mountain itself is the highest peak in the Pfalz.
Heinrich der Vogler is said to sleep in the Sudmerberg near Goslar. Goslar as my Harz born mother always used to fondly tell me was a Kaiserstadt (an imperial city). However the German king who is most often associated with this legendary motif is in fact Barbarossa.
"The German people still maintain the same faith, for their hero has been seen by many of them in the Kyffhäuser mountain, in the old palatinate of the Saxon imperial house. There, in a cavern, with all his knights and squires around him, he sits to this day, leaning his head upon his arm,at a table through which his beard has grown, or round which, according to other accounts, it has grown twice. When it has thrice encircled the table, he will wake up to battle. The cavern glitters with gold and jewels, and is as bright as the sunniest day. Thousands of horses stand at mangers filled with thorn-bushes instead of hay, and make a prodigious noise as they stamp on the ground and rattle their chains. The old Kaiser sometimes wakes up for a moment and speaks to his visitors. He once asked a herdsman who had found his way into the Kyffhäuser, 'Are the ravens' (Odin's birds) 'still flying about the mountain?' The man replied that they were. 'Then', said Barbarossa, 'I must sleep a hundred years longer.'
"That Frederick and all the rest of the caverned princes and warriors are no other than Woden and his wild host, is clear from many details of the legends concerning them. People who visit the Emperor in the Kyffhäuser receive just such presents as are given by the wild huntsman,-horses' legs or heads that afterwards turn into gold; and there is a lady in the Kyffhäuser, who is variously called the Princess, the Kaiser's housekeeper, Mademoiselle or Jungfer, and sometimes Frau Holle (Holda), who is beyond doubt Woden's wife Fria."(Curiosities of Indo-European Tradition and Folk-lore, 1863, Walter Keating-Kelly)
Tales of famous mediaeval kings can also be found in the folk-lore of other European Aryan peoples but what is significant about the legend of Barbarossa in the Kyffhäuser is the direct association with the God Woden. This is what makes the study of folk-lore so important to us. Folk-lore provides a continuation of the myths of the Eddas into post-conversion times upto the modern era.