I recently wrote about how I think horror should be defined. Rather than defining it by how the audience feels when they watch it, I focused instead on the importance of the villain’s relationship to the protagonist. The definition I landed on was based on my thinking about how predators interacted with humans throughout our evolutionary history:
Horror is the genre in which a more formidable antagonist aims to kill a less formidable protagonist.
Drawing the Boundaries of Fear
This definition is more grounded than others I’ve seen and does a better job of drawing lines between what is and is not horror. Of course, there are still some edge cases. Most of these come down to how “formidability” is defined.
In the animal literature I draw from, formidability is about resource holding ability. In other words, how likely is an animal to capture and keep some resource, whether it’s a mate, food, or territory. This is mostly based on how powerful the animal is because greater power means more ability to take and defend resources from others during conflicts.
Raw power isn’t everything. Strategy certainly exists in the animal kingdom, as do differences in intelligence. These play into formidability in others animals to some extent. However, no other animal comes close to humans in their ability to gain leverage and compete through planning and strategy.
This is where thrillers begin to be defined in relation to horror films. Whereas a horror villain leans more on traditional animal formidability when intimidating the protagonist (i.e., power), a thriller villain leans more on the human strategy component for intimidating and attacking an opponent.
However, this difference alone doesn’t distinguish horror from thrillers. If a villain was exceptionally more formidable due to their intellect or ability to out-strategize the protagonist, the film would be more of a horror film.
The Classic Definition of a Thriller
Existing definitions of thrillers tend to center on suspense or excitement. Dan Brown, author of The Da Vinci Code, argues that thrillers must center around 3 C’s:
The Crucible: The protagonist must struggle. The stakes must be high and the situation must require the protagonist to face the obstacle.
The Clock: There needs to be a ticking clock in a thriller. With every passing second, the stakes increase.
The Contract: The story must reveal the answer to the big question that is posed throughout. Thrillers need a satisfying resolution to the tension they pose.
I think this is essentially right, but it is more of a necessary set of conditions for a thriller rather than unique set of conditions for a thriller. Many drama films have similar requirements, though the clock is perhaps less important. Horror also relies on these three C’s but the contract is less iron-clad; some have a satisfying answer to the big question, and some leave you clueless.
The Protagonist-Villain Relationship
It seems to me that a key difference between a thriller and a horror story is the relationship between the protagonist and villain. In a horror story, the villain is far more formidable than the protagonist, and the protagonist is usually fleeing from the villain. In a thriller, the protagonist and villain are more evenly matched, and the protagonist is not usually running from the villain. The two are often locked in a battle of wits and strategy that resembles a chess match more than it does a predator-prey situation.
The tension doesn’t come from knowing the protagonist is likely doomed, as it does in horror, but from not knowing whether they will succeed.
This is probably a necessary but not unique feature of thrillers. Protagonists are also usually equally matched to villains in action movies. Though, in an action movie, you’re often pretty sure the protagonist will come out on top. In any case, this seems to be a good way to distinguish whether a movie is horror or thriller, two genres where films often get mixed up.
So, a first stab at a definition of a thriller might be something like:
Thriller is the genre in which roughly equally formidable opponents engage in a contest of strategy, where tension arises from uncertainty about the outcome.
This protagonist-villain framework also helps explain why some films feel like they switch genres partway through. Take From Dusk Till Dawn — it starts as a thriller about criminals and hostages (equally matched humans in a strategy contest) but transforms into horror when supernatural vampires appear (overwhelming formidability gap requiring survival tactics).


It might also explain why some horror films become less scary but more tense as they progress through a series. As protagonists gain knowledge and capabilities to fight the threat, the formidability gap closes and the dynamic shifts from horror toward thriller or action.
This happens in the Alien franchise. the first film is pure horror with a single, seemingly unstoppable alien, while Aliens moves toward action as armed marines face multiple aliens with more even odds.
I’m still thinking through this and would love to hear your thoughts, so I’ve opened the comments to all subscribers.
A diagram would be useful. If we had a taxonomy of genres how much could be explained by protagonist power difference?