Hrothogar

According to the Beowulf poem he ruled Denmark when this hero comes along to defeat Grendel. He was supposed to have built a famous hall called Heorot[?], and according to Saxo Grammaticus in Gesta Danorum, he (by the name of Roar or Ro) founded the town Roskilde. His brother Helge[?] who ruled before him had a famous son, Rolf Krake.

There are no historical facts to prove neither of these characters existence. See also Origins for Beowulf and Rolf Krake.