Enemy Within



""Pounding in your temples and a surge of adrenalin every muscle tense to fence the enemy within""

- Rush, The Enemy Within

A specific form of Split Personality. Maybe the Body Horror became a bit too fused with someone. Maybe the Unstoppable Rage is getting...too unstoppable. Perhaps The Atoner's past is taking a life of its own. A half-human's Demon/Vampire self is trying to take control, or that Deal with the Devil is hitting a bit too close to home.

Either way, the enemy is behind the hero's eyes, and its time is coming when it can take over. Until then, it'll do all it can to control him and get him to give in to its Horror Hunger. The thing to stress most is that the Enemy Within is the hero. He or she cannot simply exorcise it out. Often the Enemy Within is the cause of the powers that the hero has that allows them to do what they do. With Great Power Comes Great Insanity, remember?

Often, since Evil Is Cool and Evil Feels Good, other characters may realize the danger before the hero and need to convince him.

Contrast Enemy Without. Compare Jekyll and Hyde. Usually part of their Soul Anatomy.

Anime and Manga

 * Ichigo from Bleach regained tremendous Shinigami powers, but the method he used resulted in the awakening of a dark personality, an "Inner Hollow" within his consciousness. Throughout the series a recurring theme is having to battle this inner demon for control of his powers made stronger by their dual existence.
 * Ichigo later meets other Shinigami who, through a slightly different process, ended up in basically the same situation. They trained him in how to properly overcome and control his inner demon, but he ended up leaving before the training was complete.
 * One of The Hunter duo from Venus Versus Virus is a young girl who is an "Anti-Virus," a biological evolution against The Heartless monsters that plague mankind. However, this has resulted in a Split Personality that merely kills The Heartless first, and then turns on her partner. The Flash Forward at the beginning of the first episode implies that her two halves will become whole... but as a Face Heel Turn.
 * In the manga she eventually learns how to control her virus side and use it to her advantage.
 * The Reveal behind the Big Bad in Animerica's second season is
 * Guts from Berserk - on occasion, when he enters the eponymous Unstoppable Rage, we see a hideous black houndlike entity hovering around him. Certain characters refer to it as the Beast, and it's hinted that his humanity will be lost to it if things keep going as they currently are.
 * from My-HiME has one, and it's.
 * There's a lot of debate in the Digimon Adventure 02 fandom as to the true nature of Ken Ichijoji's Digimon Kaiser personality - how much of it was his own doings and how much of it was a result of the Dark Spore? Alternate Character Interpretation suggests that it was a Split Personality (which isn't entirely illogical when you consider how different the Kaiser and regular Ken were) but it's more suggested that Ken is an example of how even the nicest person alive can turn nasty, making him more Enemy Within.
 * (Hell, these characters are all practically an allegory for modern digital relationships on the internet. So... yeah.)
 * Ryo Takatsuki from Project ARMS literally has an Enemy Within. Specifically, within his right arm. Tick him off enough, and he turns into the Jabberwock, a massive demonic humanoid capable of mass destruction. Beware the Jabberwock my son!
 * Inuyasha has this in the form of his demon blood. Being a half demon, half human, his demon blood is considered too powerful for him to control. When it takes control, it turns him into a mindless animal that attacks purely on instinct, unable to tell friend from foe. Inuyasha's father gave him a safeguard in the form of his Empathic Weapon Tessaiga to keep it in check. As long as the sword remains in Inuyasha's possession, his demon side is suppressed, though he remains stronger than the average human for it.
 * Senri from +Anima has an similar to Inuyasha above actually.
 * In D Gray Man, it's revealed that
 * Ryo Bakura and Malik in Yu-Gi-Oh!.
 * In Dragonball Z, Majin Buu was introduced as a huge, pink, disturbingly cheerful jinn that liked to turn people into candy and eat them. However, an encounter with an injured dog and Hercule/Mr. Satan caused a Heel Face Turn. Crisis averted, right? Well, up until the dog gets shot, at which point he becomes so furious that all of his inner evil comes to life. It then eats him, becoming even more powerful than the original as a result.
 * Becomes
 * Haine of DOGS Bullets and Carnage has one in the form of a 'mad dog' due to the experimentation he suffered as a child. It overtly led to the . Arguably, all characters who have a Cerberus spine fall under this trope.
 * The eponymous character of Soul Eater deals with this, especially as it pertains to keeping Maka safe. He literally has a small ogre-demon living inside his soul. It starts to take over in the final battle with Asura (in the anime), when Maka has to, in order to save her partner from the Madness with the Power of Love.

Comic Books

 * Marvel's Sentry character housed a dark and equally powerful villain known as the Void. In his original appearances, the Void manifested as a seperate entity outside of the Sentry's body. In later appearances, the Sentry transformed into the Void. The most recent depictions show the Sentry retaining his human appearance, while his eyes turn black.
 * Malus Darkblade and T'zarkan in the Malus Darkblade series. Of course, Malus is already a very evil person and as such doesn't exactly need goading, but T'zarkan tempts him with power at the cost of more of his soul.
 * One timeline in the Marvel continuity of Transformers comic books had Rodimus Prime trapping Unicron inside the Matrix...which was located in Rodimus' chest. It wasn't pretty when Unicron managed to break free and posses the young Prime's body.
 * An issue of the French comic book Nävis features Girodouss, an alien who takes on a monstrous alterego when she gets hungry and doesn't change back until she's hunted down and devoured her prey. This is normal for her species, but Girodouss doesn't like to kill. She can only be cured of this by mating, but in doing so, she will go into one final rage and murder her mate. Fortunately, she's able to Take a Third Option.
 * Kid Miracleman.
 * Doctor Strange allowed the superpowerful entity Zom to become one of these for himself in World War Hulk, only to learn a painful lesson about how Evil Is Not a Toy.

Film

 * David Cronenberg's Remake of The Fly
 * Inception. Dom's guilt over his wife's death leads into her showing up to screw up his plans in every subsequent dream-visiting trip he does.
 * Fight Club:
 * Black Swan shows a truly horrifying example of this, culminating in both sides of the lead trying to literally KILL each other.
 * The Id monster of Dr. Morpheus in Forbidden Planet

Folklore

 * Older Than Print: Werewolves in any story in which the werewolf form is disconnected from, or uncontrollable by, the human form. There are sympathetic folktales about otherwise good people suffering from lycanthropy.

Literature

 * Rand al'Thor and Lews Therin Telamon in Robert Jordan's The Wheel of Time series. It's never made certain whether Lews Therin really does exist, or whether Rand is simply becoming insane due to the taint on Saidin and pure stress. In the eleventh book, Semirhage
 * Given the number of things he literally could not know unless the voice in his head really is Lews Therin, it's pretty certain. It also shows up long before he develops any of his other Taint-related symptoms.
 * It is now confirmed end of the 12th book.
 * Dandra in The Dragon Below trilogy has a rather complicated version in the form of the imprisoned personality of her creator, Tetkashtai.
 * Nearra in the first six books of Dragonlance: The New Adventures has one.
 * In Orson Scott Card's The Devil in Velvet, the protagonist, Nicholas, makes a deal with the Devil to return in time to 18th century England to stop a murder most foul by, in essence, leaping INTO and taking over control of the body of his ancient ancestor. But the old boy is still there, trying to get out of the box, and whenever Nicholas is extremely stressed or emotional, Old Nick jumps out, seizes control of his body, and does dastardly things until our hero can regain control.
 * Discworld's Sam Vimes contains an Unstoppable Rage ("the Beast") which he first kept in check with alcohol and then with rigid self-control. Sometimes he and the Beast have a common goal, though, such as when his family is threatened.
 * In Return of the Archwizards Galaeron Nihmedu overused the shadow magic despite his mentor's warning. This puts him into the "shadow crisis"—that is, now his "shadow self" got a foothold in him and it sucks to be Galaeron very much, in several ways at once. May be the best reply (and counterpart) to Enemy Without of Earthsea Trilogy ever.
 * The Status Civilization by Robert Scheckley. The protagonist is exiled to the planet of criminals as a convicted murderer. He doesn't believe he could have killed in cold blood but has to kill in self-defense in exile. In the end, he finds out the truth:
 * In Scorpion Shards, the protagonists are infected by otherworldly parasites that turn their superpowers to evil. Giving in to the corrupted, evil urges feeds the parasites.
 * There is a classic treatment in Julian May's Galactic Milieu Trilogy (Jack the Bodiless, Diamond Mask, Magnificat), where a principal adversary is an immaterial being called Fury that turns out to be a subconscious manifestation of a major character.
 * In the New Jedi Order series, after an attempt to brainwash her completely goes wrong, Tahiri ends up with one of these in the form of Yuuzhan Vong personality Riina Kwaad. Riina's not evil exactly, but she is very messed up and her attempts to pull a Split Personality Takeover do a serious number on both their sanities. They end up doing a Split Personality Merge instead.

Live Action TV

 * Supernatural's Sam Winchester is a sort of human/demon hybrid and constantly fights against his demonic inheritance, which includes a portion of natural arrogance, but under the right circumstances turns him completely and murderously feral.
 * Angel, and vampires with souls in general, from Buffy the Vampire Slayer and Angel. Buffyverse vampires are generally corpses of people without a soul, and thus a conscience; only the memories and intelligence of their former human selves keeps them from becoming completely feral. However, if a vampire regains their soul (as Angel did, and Spike eventually does), this trope comes into full effect: despite having a human soul again, their demonic nature is still present and has to constantly be kept in check.
 * Oz, to a lesser extent. His werewolf self isn't exactly bad, but wild and uncontrollable, and he certainly fears doing harm to someone during the full moon. He later gets Put on a Bus when he realizes that his werewolf side's beginning to affect his human personality, and sets off to find a cure.
 * Especially true in the case of Angel, who is constantly one moment of "perfect happiness" away from reverting to Complete Monster. Angelus hates being trapped in Angel since he has to deal with Angel's altruism, but takes comfort in the fact that he'll always be able to torment Angel.
 * Forever Knight has Nick Knight, a vampire trying to earn redemption as a Toronto homocide detective, struggling to suppress his predatory nature and bloodlust. Unlike the vampires in Buffy the Vampire Slayer and Angel, vampires in Forever Knight do generally have souls: most of them just give in to their new instincts fairly quickly and never look back.
 * Played with in Kamen Rider Den-O. Because the main character and his Anti-Hero rival are special individuals called Singularity Points, they can exert their will when Imagin possess them. Of course, while most Imagin are brash monsters, those bonded with the heroes are considerably mellower and end up befriending their human partners, making this more an example of Ally Within.
 * Played a bit straighter with Ryutaros, who due to being buried deep within Ryotaro's psyche for an extended period of time, is much harder to drive out. That, combined with his willful and childish nature, can sometimes cause major problems, as seen in one episode where he decided to beat the Monster of the Week by killing the human to whom it was bonded. At the end of the day, though, he's still an ally.
 * Hyde from Jekyll.
 * Crichton when possessed by the Scorpius neural clone in Farscape.
 * CSI had a metaphorical version of this with Ray Langston and his two season struggle against the dark streak he felt he had. The Unstoppable Rage variant is where it most likely fits. And it overtook him by the end of season 11 when
 * In an episode of Star Trek: Voyager, the Doctor tries to expand his program by incorporating personality aspects of various historical figures who possessed great minds. He failed to realize that he would also incorporate the darker sides of their psyches, and develops an evil split personality who takes Kes hostage.

Music

 * "Animal I Have Become" by Three Days Grace.
 * "It's the Fear" by Within Temptation.
 * "Demon Seed" by Nine Inch Nails
 * "Innocence and Instinct" by Red is more or less an entire album about this.
 * "Sad But True" by Metallica
 * "Sweating Bullets" by Megadeth
 * "Climbing Up the Walls" by Radiohead
 * "Monster" by Skillet
 * Arguably, "Down with the Sickness" by Disturbed
 * "Behind Blue Eyes" by The Who
 * "Enemy Within" by Arch Enemy

Tabletop Games

 * At the risk of too much "Trope Overdosed", Warhammer 40,000. Chaos is always recruiting.
 * To emphasize this, Imperial propaganda reminds you that "For every enemy without there are a hundred within". Of course, they're talking about the Imperium itself, but what that means is that it's teeming with heretics, so many that they outnumber those actually loyal to the Emperor a billion to one. I suppose that means that the those higher up on the totem pole think that the average Imperial subject failed math (which wouldn't be surprising). Regardless of how much it's emphasized, there's a bit a truth to it: Warhammer 40,000 has enemies within in spades, and all too often the enemy within wins.
 * Certain factions requires their members to conquer their enemy inside for them to join fully. The Space Wolves initiation rites have a phase in which you must conquer and learn to manage to maintain your beast within, or you'll turn into a Wulfen, a werewolf-like being. And not even once you have managed to pass this stage, it is not sure whether or not the curse is truly gone. Already initiated members can have the curse activate in the middle of the battlefield, and gain strength beyond even their already superhuman abilities. While this is usually temporary and the one affected will return to his normal form after the battle is over, this is the result of the curse not stabilizing completely during the initiation rites.
 * Eldar warriors must contain the curse of Khaine within them, learning to don and doff their 'war mask' on command, lest they be trapped upon the Path of the Warrior and become an Exarch, forever imprisoned within the armor of his predecessors, bound into the gestalt consciousness that is the Exarch, incapable of peace and unable to die.
 * The Harrowed in Deadlands combine this and Came Back Wrong: very rarely, a potent human soul will be dragged back into its corpse kicking and screaming by an evil spirit. The two cohabitate the deader's perpetually almost-rotting flesh, fighting for dominance on a daily basis. But, hey, they get some nifty powers. Yay.
 * Vampire: The Masquerade has a large bit of its mythos based around this - each Vampire is at least partially under the control of "The Beast," the representation of their Horror Hunger. The Beast is their id; it makes them feed, it makes them run from fire and oncoming sunlight, and it makes them Frenzy if they get scared or hungry enough.
 * The arc phrase of the game is actually "A beast I am, lest a Beast I become," which is an explicit statement that vampires are driven to do horrible things to control their inner hunger, and that trying to avoid doing those things will essentially lead to you losing control entirely and becoming little more than a mindless monster that does nothing but kill and feed like an animal. Try to be humane, try to be "good", and you'll ultimately become a far worse monster than people who are willing to kill and feed in moderation.
 * In D&D 4th Ed the Minotaurs have to struggle against releasing the beast within. So much that they adorn everything they wear and carry, and sometimes themselves with labyrinth designs to symbolize that struggle in their mind and soul.

Video Games

 * In Kingdom Hearts, Rival Turned Evil Riku fuses with the villain from the first game. He redeems, but is struggling with the darkness within in the sequels.
 * in Manhunt 2. He is a Split Personality that is planted by in order to pay off his debts. However, it went wrong.
 * Emil, the main character from Tales of Symphonia Dawn of the New World, has a bad case of multiple personality disorder, in which his usually meek self is replaced with a powerful, badass red-eyed alter-ego whenever he needs to fight. Later this side of him becomes increasingly dominant and much more of a jerk. We later find out that Emil is really
 * The protagonist of Wild ARMs 2 fuses with a demon destined to destroy the world and because of this he can use the sword destined to defeat said demon...on other villains.
 * Both Leona & Iori from the King of Fighters series struggle with the curse of their bloodlines, which at times can cause them to regress into a berserker state know as "Riot of the Blood". Leona killed her entire family when she was in the Riot, and Iori has killed or severely wounded others as well.
 * In The Very Definitely Final Dungeon of Planescape: Torment, the Big Bad traps your mind inside a magic prison, where the personalities of three of your most powerful prior incarnations -- The Paranoid Incarnation, The Practical Incarnation, and The Good Incarnation -- splinter from your mind and start interacting with you. Reintegrating with your body is only possible through subduing or uniting all four fragments until only one remains, and the Practical Incarnation isn't particularly well disposed towards letting you be the one to do this.
 * In fact, it's implied that being able to resurface and take over your body has been part of his plan all along - a means of surviving beyond death, if his initial plan to defeat the evil had failed.
 * in Neverwinter Nights 2: Mask of the Betrayer forces you to continually consume other spirits or have your soul consumed instead. The main quest of the game is figuring out a way to get rid of the curse.
 * In The Prince of Persia: The Two Thrones, the "Dark Prince" initially acts like a benign Exposition Fairy, seeming to be just like the prince, only with fewer scruples. Strangely enough for this trope, he never makes an actual bid for control over the Prince's body until the very end, spending most of his time trying to corrupt the Prince—though after the Prince rejects his help, he just petulantly taunts and distracts you during That One Level.
 * Condemned 2 has the Alcohol Demon, a manifestation of Ethan Thomas' alcoholism. At numerous occasions through the game, Ethan is tormented by the damn thing
 * The final boss in Castlevania: Aria of Sorrow is the embodiment of Dracula's evil, which threatens to possess and overwhelm Dracula's reincarnated self,
 * The Personae (of the Persona RPG series) are supernatural spirits that exist within a person's psyche, representing their unconscious selves. Hence, the more nasty Personae tend to have unpleasant effects on their host...
 * In Persona, Guido's Persona.
 * In Persona 2: Eternal Punishment, those who use the Joker Curse.
 * To elaborate, these last two examples may not really count...
 * In Persona 3, the members of Strega have Personas that actively try to kill them. To prevent this, they have to take suppressants that have nasty side-effects..
 * The Shadows. They're manifestations of humanity's worst flaws and suppressed dark thoughts. It's best shown in Persona 4, in which the protagonists each have to face shadow versions of themselves.
 * Xenogears, Fei and
 * In the eroge strategy game Sengoku Rance of the Rance series, Nobunaga is possessed by the demon known as Xaiver, after he accidentally breaks one of the eight gourds containing Xaiver's essence.
 * In Sly Cooper 3: Honor Among Thieves, The Panda King (one of the villains of the first game) is trapped within his mind of his failure against Sly. Eventually Sly himself enters his mind to convince him into an Enemy Mine and snap out of the trance to save his daughter, who's captured by a local warlord.
 * A rather weird example played for laughs is found at the end of Fallout: New Vegas DLC Old World Blues, where you confront
 * A variation is used in Metal Gear Solid: Portable Ops.
 * Ryu from Street Fighter is a Blood Knight but also surprisingly in control and an overall nice guy. Thing is, the art he learned gave way for a darker side of him that he has to keep in control. When the power activates, he's called Evil Ryu. It's still Ryu, but he's driven mad and doesn't hold back anything at all. Basically, he comes closer to being the next Akuma.

Web Comics

 * In Girl Genius, Agatha gets taken over by "The Other" (who either was or previosly possessed ). They struggle for control of her body until The Other unwittingly . Since without the locker she emerges again, and it's not clear how much memories may cross-leak, this is treated as both turn-off for her suitors and a security problem.
 * Mr. Chalk from Zebra Girl, seems to be the manifestation of Sandra's demonic taint and appears in her dreams in order to drive her to cause pain and suffering. Amazingly, he's not the one that caused her Face Heel Turn.
 * Breakfast of the Gods turns Sugar Bear's Super Bear form into one of these.
 * from In Wily's Defense.
 * In Twokinds Trace Legacy is one of these, though he's not actively fighting it... yet.

Web Original

 * Yoi, of Magical Girl Hunters has his split personality who eventually gains his own body.
 * Kickassia implies that Dr. Insano used to be this to Spoony, who eventually won a hard-fought battle for control, turning them into Jekyll and Hyde.

Western Animation

 * Raven from Teen Titans often suffered from this, being half-demon.
 * It's implied that Beast Boy went through this as well with his Super-Beast form.
 * The two actually have a little chat about this at the end of the episode where Beast Boy got said form.
 * On a very similar show, season two of Legion of Super Heroes saw Brainiac 5 discover the power available by accessing evil Brainiac 1.0's memories. But then, well, this trope. He ends up playing super-Chess in his head.