The ageing king of the Spear-Danes, he was loyal, kind, but didn’t have the strength to face with the conquerors, especially with Grendel. Also, a lot of time ago, the king paid money to Wulfings to resolve blood feud they had with Ectheow, Beowulf’s father. That’s why he welcomed Beowulf's assistance in facing demon Grendel. His sermon to Beowulf before the Great champion's departure is thematically important; his great mead-hall, Heorot, symbolizes the kingdom's success, civilization, and joy. In his day, he was a very mighty and powerful warrior. After him, Beowulf became a king.
Hrothgar in the Essays