There are many villains in the horror genre that have been very hard to kill, and some of them have never been killed and might never die.
Some horror movie villains, like Candyman and Leatherface, have proven to be incredibly difficult to kill due to their supernatural abilities or strength.
The Entity from It Follows and The Creeper from Jeepers Creepers are both immortal villains who seem to have no known weaknesses, making them incredibly formidable.
Villains like Chucky, Michael Myers, and Jason Voorhees have been killed and brought back to life multiple times, suggesting that they possess a certain level of immortality or superhuman resilience.
The horror genre is home to a variety of villains and monsters, and while many of them are defeated by the end of their movies, some have proven to be unbelievably hard to kill. Horror movies don't really have a formula when it comes to their villains and how they have to be defeated. Many movies have supernatural villains, who can be demons, spirits, monsters, aliens, or other types of creatures, and though they usually have a weakness that is key to their defeat, some have turned out to be way more complex than initially thought.
Other horror movies opt for human villains who, in theory, should be easier to defeat as they should have weaknesses, but even these villains have pushed their own boundaries and been quite hard to kill. Some others are a combination of human or animal with supernatural, which not only makes them more terrifying but also much more resistant to all the efforts of the main characters to kill them. While many of these villains were eventually killed, others have survived their movies and franchises, and they seem to be immortal.
10 Candyman - Candyman franchise
The Candyman hive makes him essentially immortal
The legend of Candyman began in the 19th century when Daniel Robitaille was punished with torture and death for falling in love with a white woman. After his right hand was cut off, he was smeared with honeycomb and left to the bees to sting him to death. Robitaille's body was later burned, but he returned as the vengeful Candyman, an entity that can be summoned by saying his name three times in front of a mirror. As such, Candyman can't be killed because he's already dead, and the "Candyman hive" has kept his legend alive.
The 2021 Candyman reboot revealed the existence of the "Candyman hive", formed by innocent Black men killed by racist authorities. Candyman assimilates with each new "candidate", thus keeping the legend alive and "fresh", ensuring that Candyman will never die.
9 Leatherface - The Texas Chainsaw Massacre franchise
Although he's human, Leatherface is surprisingly strong
Leatherface is the villain of the Texas Chainsaw Massacre franchise, and even though he has been supposedly killed a couple of times, he always comes back. Leatherface survived his first movie, The Texas Chainsaw Massacre, but in the sequel, appropriately titled The Texas Chainsaw Massacre 2, he was supposedly killed after a grenade was detonated. Leatherface returned in Leatherface: The Texas Chainsaw Massacre III, where he was left to drown but was revealed to have survived. Since then, Leatherface has survived all his movies, and as he isn't a supernatural being, his strength and supposed "immortality" can simply be attributed to physical strength.
8 The Entity - It Follows
The Entity doesn't seem to have any weaknesses
It Follows centers on Jay Height (Maika Monroe), who after having sex with her then-boyfriend, starts being pursued by an entity that only those afflicted with the "curse" can see, and which can take the appearance of any person. If the person carrying the curse is caught by the entity, they will be killed, and the entity will go after the person who passed the curse onto them. With the help of her friends, Jay comes up with a plan to kill the entity by electrocuting it in a swimming pool, but at the end of It Follows, it's revealed that the entity is still active. As the origins and more about the entity are unknown, it's, at the moment, an immortal villain.
It Follows is getting a sequel, They Follow, projected for a 2024/2025 release.
7 The Creeper - Jeepers Creepers
The Creeper's unique abilities make it immortal
The villain of the Jeepers Creepers franchise is an ancient creature simply known as "The Creeper", which awakens every 23 years for 23 days in order to feast on human body parts to regenerate its own body. The Creeper can also regenerate lost or damaged body parts by absorbing them from one of its victims, and though it has been wounded, it hasn't been killed yet. The Creeper's ability to regenerate makes it pretty much immortal, and the only way to possibly kill him would be to keep him from feeding, but that definitely wouldn't be easy.
6 Xenomorphs - Alien franchise
Xenomorphs are extremely hard to exterminate completely
Xenomorphs are endoparasitoid extraterrestrial beings that have terrorized the characters of the Alien franchise for decades. Their blood is an extremely potent acid and they reproduce quite fast, making them very hard to exterminate. Xenomorphs are also unbelievably fast, strong, relentless, and physically terrifying, as their appearance is enough to freeze anyone in fear. Even if various Xenomorphs are destroyed, if one egg or face-hugger survives (and there surely is at least one, given how fast they reproduce), Xenomorphs will continue terrorizing the Alien franchise.
5 It - IT
It is an inter-dimensional shapeshifting entity
It is an evil, shapeshifting, inter-dimensional entity that originated in a void containing and surrounding the universe. It is comprised of the Deadlights, which are a deadly eldritch form of energy perceived as radiant orange lights. This is It's true form, but as it's too complex for the human mind to comprehend (and those who see it end up losing their minds or even dying), it takes the shape of a giant female spider as its "final" form. It's shapeshifting abilities make it hard to kill, but the Losers seized its spider form and finally killed it, ending It's reign of terror in Derry, Maine.
A prequel TV series to the movies It and It Chapter Two, titled Welcome to Derry, is scheduled to be released in 2025 on Max.
4 Chucky - Child's Play franchise
Chucky has been burned, mutilated, and more
Although he's made of plastic, Chucky has been brought back from the dead many times throughout the Child's Play franchise. The "Good Guy" doll came to life after a serial killer transferred his soul into it through a voodoo ritual, and since then, he has been going on multiple killing sprees for decades. Chucky has been burned, mutilated, and destroyed multiple times, but there's always someone willing to bring him back to life - either the company that makes the "Good Guy" dolls, his former lover Tiffany Valentine, or his child, Glen. As long as there isn't anyone who wants to resurrect him, Chucky can definitely be destroyed for good.
3 Michael Myers - Halloween franchise
Michael Myers was supernatural at some point
Michael Myers was supposedly killed and brought back to life multiple times throughout the Halloween franchise, and the reasons for his return went from switching places with innocent people to a supernatural influence on Michael. Michael Myers survived being shot, stabbed, run over, and even burned alive, and in Halloween: The Curse of Michael Myers, it was revealed that his evil and immortality were the result of a curse from an ancient druid cult.
This is one of the most hated storylines in the Halloween franchise, and though Halloween Kills made him supernatural again (without any explanation), Michael Myers was finally killed in Halloween Ends after Laurie slit his throat and then threw his body into an industrial shredder.
2 The Thing - The Thing
The Thing's ability to assimilate & imitate other organisms guarantees its survival
John Carpenter's The Thing follows a group of researchers in Antarctica who come across an extraterrestrial life-form that assimilates and imitates other organisms. Because of this, there was a lot of paranoia among the group as they didn't know who was still human and who had turned into "the thing", and the creature spread so fast that it was, essentially, indestructible. It's even implied at the end of The Thing that either (or both) MacReady or Childs were "the thing", but this hasn't been confirmed (yet), so the Thing was still alive at the end of the movie.
1 Jason Voorhees - Friday the 13th franchise
Jason Voorhees is basically a zombie
Jason Voorhees has spent decades terrorizing everyone at Camp Crystal Lake (and in space, as well), and he has been shot, stabbed, and supposedly killed way too many times, yet he always finds a way to return. As Jason died when he was a child after drowning at Crystal Lake, the adult Jason Voorhees everyone knows as the villain of the Friday the 13th franchise is basically a zombie, thus why he's so hard to kill. Jason Voorhees is believed to be immortal, and it's to be seen if future Friday the 13th projects explain his immortality or give him a weakness that can lead to his definitive defeat.