In middle school my Beowulf essay was about how killing Grendel and its mother were justifiable acts because they were preying on humans, but the dragon was attacked in its lair for profit. I think we see the same flaw in the story – it suffers from sequelitus:
- Beowulf 1 – Mysterious stranger fights mysterious monster. Tight script, low budget (keeps the monster in shadows). Sleeper hit!
- Beowulf 2 – exact same story, BIGGER MONSTER!
- Beowulf 3 – the actor playing Beowulf is now a major box office star so the third film needs to be high-budget Hollywood with new locations and a spectacular CGI monster. "King" Beowulf fights Grendel's... father? Grandmother? Corporate test-marketing says dragons are big, let's go with a dragon.
- The extra dimension is given by the divergence of the world and the hero. The hero does not change, but the world does. Beowulf has always been a scheming villain, but this was accepted in the past, and now it is frowned upon. This seems to require rewriting the setup of the story, which was not my original intent.
This is the correct option, but you are not being true to this premise. First I'll show the narrative issues with your take, then I'll suggest a fix that I think is truer to the idea.
You want Beowulf to be a villain, so you ret-conned the first 2 stories. He was always a villain, but everyone was ok with it back then (before those pesky #metoo stories ruined the fun times for villains?). Beowulf has absolute power – he's the king – and like every evil despot, when the people are dissatisfied with the injustice and corruption he… leaves? To fight a dragon?
Who is the protagonist of this story? Who steps into the role of "actual hero"? The only other character you mention is a slave. Big red flag if you have a melodrama overlord with an evil plan but no protagonist. Who are we suppose to root for, the dragon? What are the stakes and obstacles of this story? Where is the conflict? Spoiler: we all know how Beowulf ends.
Most likely this is Evil Mary Sue.
To fix it, Let's start with the #1 rule of all villains: Villains do not think they are villains. We'll keep Beowulf as the protagonist and have him firmly convinced that he is the hero, rather than a melodrama villain who hasn't changed in 50+ years.
What has changed in the last 50 years? Everything! At the beginning of Beowulf, everyone lives under one roof! There is no farming, sheep are not grazing, no one is having children – these were terrorized people under siege, barely surviving. Today, post-monster, you've got two generations of worldbuilding as these people spread out and retake their land.
A lot can happen in 50 years – if you want to have smaller monsters, or wars with neighboring kingdoms, or a drama about starting a democracy, or whatever – you can attach any subplot here. But it's not necessary. What you have is a generational shift. It's built-in, you don't even need a pretext for the change. The elders who remember the time of monsters are now over 60 and retiring. Their 40-something children grew up in the boom years immediately after the time of monsters when everything was growth and reclamation. Grendel's mother didn't just eat people, she ate other monsters – she was a monster's monster. The land the Boomers inherited was fertile and monster-free. There were no limits.
The next generation, the 20-somethings, are coming of age in a time of diminishing returns. The land has been conquered and the boundaries are well drawn. The only threats to the people are internal, themselves. Boomers scheme for more, and the 2nd generation have become pawns in the consolidation of wealth. They are starting to have children, a 3rd generation far removed from those days when every life was precious. What kind of world will they inherit?
Beowulf hasn't changed. The people have. Whose fault is it? Beowulf's.
- Bonus #3 The extra dimension is a result of the hero's actions.
You have an aging hero who did the right thing, a long time ago in a simpler age. "Simpler" not because ye olden days were inherently naive about corruption, but because there were actual monsters eating people – these younger generations have no concept of how humans had to pull together to survive. They never learn to compromise, they see their neighbor as an enemy, their worst fear is that they should have less than another. Spoiled and soft, petty and selfish. They are the idealogical opposite of the people he saved, and loved.
Beowulf was the hammer that hit the nail, unfortunately the current problem is a screw. Beowulf is failing as a king. He has no idea how to steer his people through this moral crisis, and worst of all, it is the consequences of his own actions. All Beowulf knows is that he stepped into this role of "hero" in the darkest time, and times are dark now – ergo: something-something the people need a hero... and a monster to fear, to bring them together.
"You, Slaveboy! Go stick a horn in that sleeping dragon. I need to save my people."
The rest of the story is a negative change arc. Beowulf needs to step aside, he is no longer the hero the people need. Introduce a potential antagonist who maybe is the hero they need, but Beowulf can't see it. Instead he insists on a quixotic quest to provoke a dragon – something that is so far removed from the needs of his people, but plays into Beowulf's narcissism. His idea of a hero is, well, himself. He can succeed in this quest and still lose by unravelling every heroic trait one by one.
History is written by winners, and since Beowulf wins you can treat his story as a tragic king who can't let go of power, as a self-corrupted hero who loses the values he is fighting for, or if you really want a full-villain reveal there is no dragon it's all been a false flag – it begs the question whether there was ever a Grendel, or a Grendel's mother. Maybe Beowulf manufactured them too. Taken too far, it destroys all story coherency (why become dissatisfied if the goal was always to live it up at these people's expense?). I think your best narrative is in exploring Beowulf's negative turn, not in ripping off a rubber mask to reveal he was Red Skull™ all along.