First Appearance: Captain Marvel v1 #20 (August 2001).
Appearances: Captain Marvel v1 #20, 21
Years Active: In our timeline, circa 6th century C.E. In Marvel time, who knows?
Beowulf, of course, was the King of the Geats, the mighty slayer of monsters in the Danish Kingdom of Hrothgar.
Captain Marvel #20 & #21 showed the mother of Grendel, the first of Beowulf's three mighty opponents, being summoned to the modern era. Beowulf is referred to as having actually existed.