Beowulf ruled for fifty winters (years) in Geatland before the dragon was disturbed. Beowulf ascended to the throne after his cousin, Higd's son, was killed.
Beowulf rules the Geats for fifty years. At around line 2210, the poem says that after the death of Hygelac and his son Heardred, Beowulf ruled well “for fifty winters, grew old and wise / as warden of the land.” For those fifty years, Beowulf lived an exemplary life; he behaved with honor, did not cut down a comrade who was drunk, and controlled his tremendous strength.
It is after this protracted period of prosperity that Beowulf’s final challenge, the dragon, appears. Someone has broken into the dragon’s lair and stolen a jeweled goblet, enraging the dragon. The dragon lays waste to fortifications up and down the coast, and even destroys Beowulf's own throne room. Beowulf chooses not to raise an army to fight the dragon, figuring that he and eleven companions should be able to defeat the monster.
After Beowulf defeated Grendel at a battle in the mead hall of the Danes, Grendel's mother sought to avenge her son's death. She attacked the mead hall after sunset and killed King Hrothgar's confidant and warrior. The King was furious and sad and asked Beowulf to pursue Grendel's mother to her hideout. Beowulf pursued the monster and defeated her in a great battle at her hideout. After this achievement Beowulf and his men went back home.
Beowulf then became king of the Geats after the fall of King Hygelac and his son Heardred in a battle with the Swedes. Beowulf went ahead to rule for 50 winters (years) peacefully before the kingdom was attacked by a dragon.
"He held it well, ruled fifty winters; he was an old land guardian.Then in the dark nights a dragon began to rule, he who guarded a hoard, a steep stone burial mound high on the heath."