The monster of a Danish lake. Grendel plagued the King of Denmark by assuming human form, forcing a way into the palace each night, and killing some of the king's people. Eventually the monster forced the king to abandon the palace, which remained empty for twelve years until the Swedish hero Beowulf heard about Grendel. The king was glad to accept and offer of monster extermination, and Beowulf sailed for Denmark with fourteen companions.

They took up residence in the deserted palace, where the king treated them to a feast but hurried away at nightfall. Beowulf kept watch while his companions slept, but the night was so quiet that he had begun to doze off when the monster crashed through the great barred doors of the palace.

Wet and slimy from the lake, and snarling in anticipation of fresh victims, it charged towards the sleeping men. Beowulf leapt to attack it without even taking time to snatch up his weapons, and in furious struggle he tore off the monster's right arm. Grendel left his bleeding arm in Beowulf's grasp and escaped through he shattered door, with the Swedes in hot pursuit until the bloodstained trail endedon the shores of the lake.

They felt certain the monster would not return, and with great rejoicing the king and his nobles returned to the palace. But on the following night Grendel's mother smashed a way into the palace to seek revenge. She was even more terrible than her son and she killed and carried off one of the Danes, with Beowulf close on her trail. When she plunged into the lake he dived after her, and found himself in a great vaulted chamber under the water. Grendel's mother attacked him savagely, but he was now armed with his sword and after a bloody duel he ran her through.

The corpse of Grendel lay in the underwater chamber, and Beowulf made doubly sure that the monster would not trouble the king again by cutting off the head and bearing it triumphantly to the palace.