Heoroweard is a character who appears in Beowulf and also in Norse legends, where he is named Hjörvarðr or Hiartuar. If he existed in real life, his name would have been Proto-Norse *Heruwarduz[1].
In the Norse sources, Hereoweard rebelled against Hroðulf/Hrólf Kraki and killed him, but otherwise the sources vary greatly. This is an account of the differences:
In the paraphrase of Bjarkamál in the Gesta Danorum of Saxo Grammaticus, his army consisted of Swedes in one line and of Geats in another line. This information does not appear in any other sources.
Several sources mention that he was married to Skuld, who according to Angrim's summary of the lost Skjöldunga saga was the daughter of Aðils the Swedish king (called Eadgils in Beowulf). However, according to the Chronicon Lethrense and Hrólf Kraki's saga, she was the daughter of Helgi (Halga), whereas Saxo is vague whether it was Adils or Helgi who was her father.
Hrólf Kraki's saga does not mention where he came from, but according to Arngrímur Jónsson, Heoroweard was the king of Öland and according to Saxo, he became Hrólf's jarl in Sweden, whereas in the Chronicon Lethrense, he was German and the jarl of Skåne.
In Beowulf, he is the son of Heorogar, the elder brother of Halga (Helgi) and Hroðgar (Hróar). (Consequently, he had greater right to the Danish throne than Hrólf Kraki (Hroðulf), and it is not surprising that he was the one who slew Hrólf.) He is mentioned only once, at lines 2160-2161. Beowulf, in the act of giving to his lord Hygelac the armor of Heorogar (which Hrothgar had given to Beowulf as a reward), repeats what Hrothgar told him: "No sooner would Heorogar give it to his son, valiant Heoroweard, though he was true to him..."
He did not survive long after Hrólfs death. According to Arngrímur Jónsson's epitome of Skjöldunga saga, Hrólf Kraki's saga and the Chronicon Lethrense, he was killed shortly after. According to Hrólf Kraki's saga, he was killed during the battle, and according to the other sources, he became king but was killed the same day.