Two major themes of Beowulf are identity and leadership.
During the time period in which Beowulf takes place, the medieval Germanic culture was dominated by tribes and large families. At the epic poem begins, all male characters are introduced based on who their fathers are. Seemingly the only way characters describe their identity is through their family lineage, which gives them a place in society. This lineage also helps set the standard by which characters live up to. Characters are proud of their successful ancestors and strive to act as valiantly as them. Beowulf initially agrees to fight Grendel as repayment because King Hrothgar offered protection to his father.
The antagonist of the narrative, Grendel, does not belong to a tribe, but is described as a descendent of Cain, so while he does not have a place in society currently, the idea of lineage is still present.
Next, the theme of leadership is examined through both Beowulf and King Hrothgar. These two characters are both good leaders in different ways. Beowulf is a fearless warrior who puts his life at risk for personal glory, which represents young leadership qualities. The older Hrothgar does not fight in hand-to-hand combat, but rather focuses on the protection of his people by enlisting men like Beowulf, which shows a more seasoned view of leadership.