Without a specific year it's difficult to say, since there has been 52 kings (and 2 ruling queens) in historical time plus an number of prehistoric kings. All the historical rules are blood related which makes the Royal family the oldest of the world's current royal houses. Further info on http://kongehuset.dk/english/history/lineage/
"King of the danes" could be interpreted as the danish head of state. The current head of state is Queen Margrethe II.
King Alfred Was the Wessex King During the Battle of the Wessex People and the Danes
wife of the king of the Danes
In Beowulf, the Danes are a tribe ruled by King Hrothgar. They live in Heorot, a great mead hall that is attacked by the monster Grendel. Beowulf comes to help the Danes by defeating Grendel and his mother.
JOSEPH
paid the Danes to leave them alone
Scyld, the great-grandfather of Hrothgar, was the legendary king of the Danes. He is described in the Old English epic poem "Beowulf" as the founder of the Danish royal lineage.
resistance to Danes
Higloc, king of the Geats and Beowulf's uncle.
Currently there is no Danish King, Queen Margarethe II is the current Danish Monarch.
The main kings mentioned in Beowulf are Hrothgar, king of the Danes, and Beowulf, prince of the Geats who later becomes king. Other kings mentioned include Hygelac, Beowulf's uncle and king of the Geats, and Hrethel, Hygelac's father.
Beowulf comes from the land of the Geats to offer his help to King Hrothgar of the Danes, who is plagued by the monster Grendel. Beowulf volunteers to defeat Grendel and rid the Danes of this menace.
King of Danes Prince of the Danes Son of Healfdene thy lord friend of Danes prince of Scyldings the giver of rings the renowned ruler danish prince gracious master