Question: how did hrothgar become king?
Answer: Beowulf tell Hrothgar that if Grendel defeats him, the Danish king should send the mail of his armor to Higlac, and return the inheritance he had from Hrethel. ... Hrothgar's older brother, Hergar, was king and died, making Hrothgar king. Hrothgar worked with Beowulf's father, Edgetho, to secure an earlier peace.