I remember reading the story of Holger Danske in a picture book when I was little: The story said that he was a great knight who now sleeps under the castle of Kronborg in Denmark, waiting to wake up and return when he is needed.
Ogier the Dane (French), or Holger Danske (Danish) is a hero from medieval romances of chivalry. While the stories claim he was a Danish prince, most of the romances in which he is featured are French and Italian. I read a prose version of his story based on a French romance (Chevalerie d'Ogier de Denamarche) written in the early 13th century.
Ogier grows up as a hostage in Charlemagne's court and becomes one of his greatest paladins (and makes friends with legendary characters such as Roland and Olivier). If you like the legends of King Arthur and the Knights of the Round Table, definitely read more about this court as well!
Ogier is strong, brave, and honorable - the very image of chivalry. What is even more important, though, is the gift given to him by the fourth fairy: “Lest all these gifts serve only to betray, I give you sensibility to return the love you inspire.” That's a very good quality for a hero.
The legend of Ogier the Dane has pretty much everything you would expect from a medieval romance of chivalry: Epic battles, daring duels, enchanted love, magical voyages, and even a trip to the Holy Land.
One of my favorite parts is the duel between Ogier (merely a day after he has been knighted) and the King of Mauritania, the Saracen Carahue. The son of Charlemagne, Charlot (who is very Mordred in a lot of ways) is also scheduled to duel with Carahue's cousin, but he decides to plan an ambush instead and get rid of the enemy, as well as Ogier (because he is jealous of his father's love for the young knight). Seeing the ambush Ogier and Carahue stop their duel and fight side by side - for chivalry, and against treason. They end up saving each other's lives and becoming best friends. Carahue keeps showing up over the course of the romance to save Ogier or help Charlemagne against other Moorish armies. It is a remarkable moment in the legend where honor and friendship trumps cultural and religious differences.
Another favorite character of mine is Turpin, who "occasionally recalled to mind that he was an archbishop." He is a priest, but also a knight and a warrior, and a very clever man - Charlemagne's most trusted adviser. He saves Ogier's life when he is imprisoned: The king plans to starve him to death by only allowing a quarter loaf of bread and a quarter cup of wine a day. Turpin, keeping to the word of the law, starts making loaves from two bushels of flour, and makes a cup the size of a barrel, keeping Ogier well fed. He is a fun, clever, likable character, and I have loved him since I read a folktale about him saving Charlemagne from enchantment (Aix-la-Chapelle: The Magic Ring).
Ogier has a wife, and a hundred-year enchanted love affair with Morgana, but the most touching love story happens at the end of his tale: After missing almost two hundred years of French history, he returns from Avalon to find Hugh Capet on the throne. He is introduced to the young queen, who is very curious about Ogier's stories and the history he lived; he tells her all of his life, and they fall in love through long conversations. When Hugh Capet dies, Ogier proposes to the queen... But sadly, the marriage never comes to pass.