While the exact time period of Beowulf's composition is debated, it's generally accepted to be written in the 8th century and depicts events set in the 5th and 6th centuries.
Though not set in England proper, the poem features a warrior named Beowulf who sails to Denmark and fights the monstrous Grendel and Grendel's mother. Beowulf then returns to his homeland (likely what is now Sweden) and later faces a dragon.
Beowulf is considered the most important surviving work of Old English literature and is a cornerstone of English literature.