"He was of a race of monsters
Not only is Beowulf the oldest known piece of English literature (written sometime before the 10th Century), but it features the first non biblical literary monster, Grendel. Grendel was a badass like no other. Coming in to a warrior stronghold at night, he rips 30 of them to shreds as if they were wet paper dolls, Grendel was one wicked dude. I've seen him represented as a giant dragon looking guy, and a savage beast (as pictured above). The epic poem leaves his appearance to your imagination. It's mentioned that he's a descendant of the original murderer, Cain, himself, so his evil has festered through generations.
Though you can read the original text (as pictured above) if you CLICK HERE, I highly recommend this modernized adaptation by Dr. David Breeded (and quoted under the lead picture above) for a better thrill, as it explains much within the text in simpler terms that would normally require a ton of footnotes.
So before Preadator, Alien, The Terminator, even Frankenstein or Dracula, you've got this wonderful creature, hundreds of years in advance, laying the groundwork for evil mayhem for centuries to follow.