The Gesta Danorum
Saxo Grammaticus in his Gesta Danorum presents three different Danish monarchs named Dan, either splitting up a single monarch into many, or properly keeping separate what others have confused.
Saxo begins his history with two brothers named Dan and Angul, sons of one Humbli, who were made rulers by the consent of the people because of their bravery. They were not however called "kings", as that usage was not then common.
Angul is the eponym of the region of Angul and from his people eventually came the English who gave their name to England. Dan fathered two sons, Humblus and Lotherus, by his wife Grytha.
Neither one is otherwise known, though a king named Humli is a leader of Huns in the Old Norse Battle of the Goths and Huns. Lotherus might have some relation to the Norse god Lóðurr or to the exiled king Heremod mentioned in Beowulf or to both. According to Saxo, Lotherus is father of the famous hero Skioldus.
The second king called Dan appears much later in Book 4, as the son of Uffi son of Vermund, (that is Offa of Angel son of Wermund). But Saxo passes over him in a few lines as a warlike king who scorned his subjects and wasted his wealth, much degenerated from his ancestors.
He is followed by King Huglek, then Fróði the Active, who is then followed by the third Dan. Apparently this Dan is the son of Fróði the Active, though Saxo does not specifically give the parentage of any of these kings. Of this Dan, Saxo relates only an anecdote that when Dan was twelve years old, tired of the arrogance of Saxon ambassadors who demanded tribute on pain of war, he bridged the river Elbe with ships, crossed over, and won a great victory.
This Dan is father of Fridlef father of Frothi, in whom one recognizes Fridleif and his son Fróði mentioned often in Norse sources, the latter being, at least by parentage, the Peace-Fróði whom Snorri introduced in the early in the Ynglinga saga.
Read more about this topic: Dan (king)