Halga, Helgi, Helghe or Helgo was a legendary Danish king living in the early 6th century. His name would in his own language (Proto-Norse) have been *Hailaga (dedicated to the gods).
Scholars generally agree that he appears in both Anglo-Saxon (Beowulf) and Scandinavian tradition (Norse sagas and Danish chronicles). In both traditions, he was a Scylding, the son of Healfdene and the brother of Hroðgar. In Beowulf, his relationship to Hroðulf is not explained, but if he was not his father, as in the Scandinavian tradition, he was at least his uncle. Both traditions also mention his family's feud with Froda and Ingeld.
Whereas, not much is said about Halga in Anglo-Saxon sources, much more is said in Scandinavian ones, all of them containing a version of the story of his incestuous relationship with his own daughter Yrsa. This liaison resulted in Halga's son Hroðulf.
Read more about Halga: Beowulf, Chronicon Lethrense and Annales Lundenses, Gesta Danorum, Hrólfr Kraki's Saga, Skjöldunga Saga and Bjarkarímur, Ynglinga Saga