Raven Software licensed the ''VideoGame/{{Doom}}'' engine from id Software to create ''Heretic'', a medieval-fantasy-themed FPS released in 1994.

The Serpent Riders, three powerful evil beings, have enslaved the seven human kings and turned their subjects into their puppets. The Sidhe Elves, of which the player character Corvus is a member, remain unaffected by the Serpent Riders' magic powers and are declared Heretics, to be wiped off the face of the earth. The Sidhe respond by extinguishing magical candles that weaken the seven kings' armies but also the Sidhe themselves. The Serpent Riders opportunistically destroy the Sidhe elders and force the rest of them into hiding.

Your task as Corvus is to seek out the weakest of the three Serpent Riders, D'Sparil, and destroy him. The other two serpent riders, Korax and Eidolon, would later be destroyed in the game's sequels, ''VideoGame/{{Hexen}}'' and ''Hexen II''.

The gameplay differs from ''Doom'' seemingly only in setting (medieval fantasy vs. futuristic military/hell). The levels follow the same formula of "get yellow key to open door to green key which opens door to blue key which leads to exit." The original order-by-mail full game consists of three episodes of eight normal and one secret level, with two more added in a licensed retail version (''Heretic: Shadow of the Serpent Riders'') vis-a-vis The Ultimate Doom.

The weapons seem to be medieval fantasy-themed edits of ''Doom'''s arsenal: An Elven Wand for the pistol, the Ethereal Crossbow for the shotgun, the Dragon Claw for the chaingun, the Phoenix Rod for the rocket launcher, the Hellstaff for the plasma rifle, and lightning-shooting Gauntlets of the Necromancer for the chainsaw. There is no direct equivalent to the BFG, and the player is instead offered the rapid-firing Firemace (which fires bouncing metal spheres, which, when [[QuadDamage using a Tome of Power]], can kill most enemies in one shot).

One notable addition was the inventory system, which allowed the player to carry items to be used later at will. Among these are the health-pack Quartz Flask and Mystic Urn; hourglass-shaped Time Bomb of the Ancients; a simple Torch; the Tome of Power, which gives your weapons new and more powerful attacks for a limited time; and a magical egg, Morph Ovum, that turns any enemy it hits into a chicken.

Heretic also upgrades Doom's "2.5D" engine to nearly-3D: the game allows you to look up and down - and failing to do so when attacking an enemy above or below your level means your shot will ''miss'', unlike in Doom where all interactions are really done in 2D. A powerup also enables the player to fly for a limited time. It's still not possible to create a room above another room, or objects like ledges or bridges that can be passed over ''and'' under.

Enemies included flying red gargoyles, golems, undead warriors, ophidians, disciples of D'Sparil, and were-dragons, each with melee and ranged attacks of varying power, and the melee-only Sabreclaws. Similar to ''Doom'''s use of Barons of Hell as bosses for one episode and then sub-bosses later on, the giant floating skull-like Iron Liches populate the later episodes. Standing in for the Cyberdemon are the Maulotaurs, giant minotaurs with fireball-slinging hammers.

The game spawned three sequels:
* ''VideoGame/{{Hexen}}'' (1996) - The player plays as one of three character classes to hunt down the second Serpent Rider, Korax.
* ''Hexen II'' (1997) - Uses the Quake engine, unlike the Doom engine of its predecessors. Four different character classes hunt down the third and final Serpent Rider, Eidolon.
* ''Heretic II'' (1998) - Based on a modified Quake II engine. Unlike the previous games, uses a third-person view. The protagonist from the first game, Corvus, must stop a mysterious plague that has decimated his homeland.

[[http://store.steampowered.com/app/2390/ Available on Steam for use with DOSBox.]]

!!'''This Game Is An Example of the Following Tropes:'''
* AllLowercaseLetters: everywhere, where possible.
* AllThereInTheManual: The backstory.
* AwesomeButImpractical:
** The powered-up Fire Mace deals exactly 10,000 damage (18-144 on bosses) and can therefore kill a non-boss monster with one sphere. However, the spheres move and bounce around very slowly, will disappear if they strike a wall before hitting a monster (terrible in tight halls), do not bounce on liquid, flying enemies generally are immune unless you fire point-blank, and ghosts are completely immune to the weapon. The weapon also follows the player's inertia complicating aiming. To top it off, the unpowered mode is like a worse version of the Hellstaff, thanks to pitiful range and zero effect on ghosts. At least it's fun to use the machine gun or power mode on weaker enemies for a laugh.
** The powered-up [[EmergencyWeapon staff]], in Heretic 1, gains a lightning aura at the tip, and works similar to Doom's berserk punch. However, the range is still pitiful, the weapon still can not affect ghosts, and the attack is less than half as strong as Doom's berserk punch (it will kill a basic golem in one hit if you're lucky). Unlike Doom's berserk, there is also an opportunity cost as you're using this weapon instead of a more powerful short-range option with your Tome of Power such as the crossbow (plenty of ammo available in the five episodes), or the longer-range Gauntlets of the Necromancer (which also heals you while zapping foes). It is decent against Sabre Claws since it pushes them away so they can't melee you, but you'll likely have a more practical weapon out and may as well use that.
* BagOfHolding: The namesake appears as an item which allows you to [[AmmunitionBackpack hold extra ammo. And gives a little bit of ammo for (almost) every weapon.]]
* BagOfSpilling: Aside from the "lose all your weapons between episodes" shtick that was pretty common back in the day, ''Heretic'' also let you only carry one of each inventory item to the next level, except for the Wings of Wrath which you just plain lost. On the other hand, this means you're encouraged to use your items as you get them, thereby averting TooAwesomeToUse.
* BalefulPolymorph: The Morph Ovum, Porkalator and Seal of the Ovinomancer items in the first three games of the series. In the multiplayer for ''Heretic II'', the Morph Ovum can be used on players. Using the Tome of Power after you've been turned into a chicken will turn you into a ''giant chicken''. This doesn't work in the first game, where the tome just turns you back to normal.
* BigBad: D'Sparil, the first of the Serpent Riders.
* BlowYouAway: The Iron Lich's windstorm attack.
* BoringButPractical:
** The Elven Wand that you start with has its own exclusive ammo (unlike Doom's pistol / chaingun), so it can be use to finish off weakened enemies in order to save ammo for your more powerful weapons. Power it up with a [[QuadDamage Tome Of Power]], and it can be used like an automatic shotgun, with best results at close range thanks to all of the shots landing and causing a CycleOfHurting for most monsters. Because it is a totally magical weapon, the wand is 100% effective against ghosts.
** The Ethereal Crossbow is gained almost immediately upon starting an episode, and acts as Heretic's [[ShotgunsAreJustBetter Shotgun / Super Shotgun]]. With plentiful ammo and Tomes of Power being quite common, this weapon can be your close-range workhorse for the entire game. The weapon is also very ammo efficient, making hard to run out.
* CallBack: To one of the earliest iD Software games, a 2D top-down maze called ''Catacomb''. Level 12 of ''Catacomb'' was called "Tomb of Desparil".
* CherryTapping: ''Heretic II'' lets you use Morph Ovum against other players in multiplayer, but a good player can still get in your face and peck you apart even then. Helped by the chicken form being small and hard to hit.
* ClassicCheatCode: As a twist, IDDQD and IDKFA, the iconic ''VideoGame/{{Doom}}'' cheat codes, [[NoFairCheating instead (respectively) kill you and rob you of all your weapons except a staff]].
** ''Trying to cheat, eh? NOW YOU DIE!''
* ColorCodedForYourConvenience: An unusual example in the keys. The yellow key is the first you collect, followed by the green, and the blue one afterwards to get to the end of the level, ''in all levels '''without a single exception'''''. By this point, it's such a firmly-rooted tradition that you'd be hard-pressed to find a custom map on any fan-made WAD that has the keys in a different order.
** ColorCodedMultiplayer: The players are red, yellow, green, and blue.
* ContractualBossImmunity: Not surprisingly, OneHitKill abilites will not work on bosses. The [[BalefulPolymorph Morph Ovum]] does nothing, but at least the powered up Fire Mace does 18-144 damage in lieu of [[FixedDamageAttack 10,000 damage]].
* ConvectionSchmonvection: Besides the usual case of lava not hurting you unless you walk on it, "The Ice Grotto" level has [[http://i.imgur.com/xTGFr.jpg ice pathways atop seas of lava.]] Try figuring that out.
* CoversAlwaysLie: Sure, you can use magic wands to kill off your enemies here, but you will see neither the glowing-blue crystal wand nor the skeletons past the title screen. And the game's packaging, too.
* [[ShotgunsAreJustBetter Crossbows Are Just Better]]: With plentiful arrows and a devastating mode with the Tome of Power, the Ethereal Crossbow is excellent for firing a burst of damage at a target before strafing into cover and repeating the process until dead. A shotgun and super shotgun in disguise.
* DamageSpongeBoss: Maulotaurs are fairly easy to avoid if you have enough space to move around in. However, they have an absolutely obscene amount of health, and you can deplete much of your ammo reserves just taking down ''one'' of them if you don't use a Tome of Power.
* DamnYouMuscleMemory: In ''Doom'', the Rocket Launcher is placed in slot 5 while the Plasma Rifle is placed in slot 6. However, ''Heretic'' places the Phoenix Rod (its equivalent to the Rocket Launcher) in slot 6, while the Hellstaff (its equivalent to the Plasma Rifle) is placed in slot 5. Just try to ''not'' get them mixed up after playing ''Doom'', especially since the Phoenix Rod can still cause SplashDamage to yourself.
* DegradedBoss: Iron Liches and Maulotaurs are met in regular gameplay after their boss introduction. So after Episode 3 (Where you fought D'Sparil), bosses are ''large groups'' of them.
* DescendingCeiling: A frequent trap. Like VideoGame/{{Doom}}, instead of being caught in a room with a descending ceiling, there's crushing traps lining certain walls or rooms.
* DifficultySpike:
** The two episodes added in ''Shadow of the Serpent Riders'' ramp up the difficulty. [=E4M1=] alone has a Maulotaur and a whole posse of Iron Liches, and not a lot of weapons or ammo to go around. Later levels have ''at least'' two Maulotaurs and five Iron Liches, sometimes all nearby each other.
** Episode 1 isn't much to write home about difficulty wise, until you get to the Citadel, which throws hordes of enemies at you from every direction (with lots and lots of Gargoyles sneaking up on you.)
** Episode three has this to a lesser extent, with at least one Iron Lich per level on the higher difficulty settings, but that's still a lot more manageable than the new episodes.
* DualBoss: On the easier skill, the Iron Liches and Maulotaurs are the bosses of the first two episodes. If you increase the difficulty, they appear in a pair or triplet.
** In the expansion ''Shadow of the Serpent Riders'', the episode's final level has at least 8 of these bosses on the hardest difficulty.
* DyingCurse: D'Sparil utters one upon his death at the end of the original ''Heretic''. It turns out to be the reason for the following two episodes in ''Shadow of the Serpent Riders,'' and its full effect is seen at the beginning of Heretic II''.
* EnemySummoner: D'Sparil spawns his disciples.
* ExpansionPack: ''Shadow of the Serpent Riders'', which added two more episodes to the three-episode ''Heretic''.
* ExplodingBarrels: Takes the form of strange plant pods (or, as they're called officialy, gasbags). For even more fun, some clusters grow back.
* FirstPersonShooter
* FlunkyBoss: One of the main things that distinguishes D'Sparil from Korax and Eidolon is that he constantly teleports away while summoning mooks to help him, instead of just straight up trying to tank you like the later Serpent Riders do. Korax does this to a lesser degree, where he only teleports away once and opens doors to {{Monster Closet}}s, but D'Sparil is much more annoying in this regard.
* {{Gorn}}: Some attempts in the manual, and enemies do tend to die messily in the game as well.
* GoneHorriblyWrong: Turns out that when you're using a series of seven [[AmplifierArtifact Amplifier Artifacts]] to cast a spell turning your entire race into [[PhysicalGod physical gods]], and one of those seven artifacts has gone missing, a duplicate will ''not'' suffice. Morcalavin, the [[spoiler:FinalBoss]] of ''Heretic II'', finds this out the hard way.
* HailfirePeaks: "Episode 2: Hell's Maw" takes place on the sides of a volcano, according to the world map, but some levels contain icy areas in addition to the usual lava pools. There is even a SecretLevel titled "The Glacier", that takes place near the bottom of the volcano, reinforcing the "fire and ice" theme of Hell's Maw. The Ice Grotto level of Episode 2 stands out with a [[SlippySlideyIceWorld slippery]] [[ConvectionSchmonvection ice lake right next to molten lava.]]
* HarderThanHard: Black Plague Possesseth Thee difficulty level makes enemies way faster.
* HealingPotion: Crystal vials, quartz flasks, mystic urns. The latter two you can carry with you.
* {{Hellgate}}: [=E1M8=] and Episode 2 are both named "Hell's Maw".
* TheHeretic: [[ExactlyWhatItSaysOnTheTin Our hero.]]
* HeroicMime: At least until ''Heretic II''.
* HumanoidAbomination: D'Sparil, though this isn't fully explained until VideoGame/{{Hexen}} II.
* HyperspaceArsenal: What's beneath that cloak? A crossbow, several staves, enchanted orbs and disks, torches, numerous tomes of power, up to sixteen hourglass-shaped bombs, and [[ArsonMurderAndJaywalking eggs]].
* IdiosyncraticDifficultyLevels / YeOldeButcheredeEnglishe: "Thou needest a wet-nurse," "Yellow-bellies R us," "Bringest them oneth," "Thou Art a Smite-Meister," and "Black Plague possesseth thee."
* IDontLikeTheSoundOfThatPlace: "Hell's Maw."
* LastOfHisKind: Corvus isn't ''quite'' the last of his kind, but the remaining Sidhe elves have all gone into hiding.
* LethalJokeItem: The Fire Mace is a weird short-ranged "machine gun" that is completely ineffective against ghost monsters, and against most monsters, isn't any better than using the Hell Staff (Plasma gun). Also, if the floor texture is water, the shots will sink. However, if you power it up, then it shoots bigger, slower spheres that will OneHitKill anything excluding boss monsters. Oh, and the big spheres ''travel through teleport pads''. It still will not hit ghosts however.
* LevelMapDisplay: In tan and sepia, to look like an ancient scroll. There's also a map scroll that reveals the entire map.
* LudicrousGibs: An unusual variation: aside from one single exception, ''every enemy'' gets shredded on the kill shot, no matter how much damage is done or what weapon is used. The exception is the Weredragon, who falls to the ground bleeding profusely from several holes, and even then it can be gibbed if dealt enough overkill damage. The Gargoyle, TheGoomba for the game, gibs in two ways: if killed normally, it falls to the ground and breaks apart with a slick "splorch" sound, and if killed with excessive force, it'll get ripped apart into smaller pieces ''before'' falling silently to the floor.
* MeaningfulName: The Greek name for the common raven is ''corvus corax''.
** Another name for a sledgehammer is a "maul", hence the Maulotaur. This may also qualify as a PunnyName.
* {{Mondegreen}}: The Disciples of D'Sparil seem to alternate between saying "He's steppin' out [[SuperMarioBros Yoshi]]" and another phrase which sounds slightly rude; D'Sparil himself appears to say "I've seen Mr. Davros". All of these are actually English phrases reversed.
* NamesToRunAwayFromReallyFast: D'sparil is pronounced like Despair-il.
* NoFairCheating: More savvy players might be tempted to try ''Doom'' cheats, since this game runs on the same engine. ...Only to discover they usually do the opposite of what you expected (e.g. Using Doom's GodMode cheat instantly kills you, while using the cheat that gives you all weapons instead takes away all your weapons and leaves you with just the staff).
* NonIndicativeName: [=E4M6=] is "[[http://doom.wikia.com/wiki/E4M6:_Halls_of_the_Apostate_%28Heretic%29 Halls of the Apostate]]" -- rather strange, given that ''you'' (the player) are the Heretic and hence the Apostate, and any halls you might have are either millions of miles away on another planet, or in another dimension.
* NoOntologicalInertia: After D'Sparil's death his entire army kicks the bucket... except for those remaining in his own plane, hence the ExpansionPack.
* NoSell: D'Sparil can teleport at will and likes to do so just before your shots hit him. Plus, he and the Maulotaurs take greatly reduced damage from normally {{BFG}}-caliber weapons like the powered-up Hellstaff and Firemace, and are unaffected by splash damage.
* OneManArmy: Corvus marches through hordes of D'Sparil's minions, through hell and back to get at D'Sparil, and then through the rest of D'sparil's army trying to find his way home.
* PowerupLetdown: Like ''VideoGame/{{Doom}}'', the Shadowsphere causes enemies to fire shots wildly. While useful if you stand still, it actually makes projectiles harder to dodge, especially in large groups. One advantage it does have is that certain physical attacks (Like the undead warrior's axes) will pass right through you.
* PuzzleBoss: The final boss of Heretic II can only be temporarily defeated through use of force. But if you don't execute a certain action in the room in the very small window of time he's down, he'll get back up, regenerate his health back to 100% and you'll get to fight him all over again.
* QuadDamage: The Tome of Power, which came out before [[VideoGame/{{Quake}} Quake's]] namesake. While some weapons simply get a damage and/or a spread boost (Firing three shots for the price of one), many weapons [[SecondaryFire work in brand-new]] (And very devastating) ways. Notably, the rocket launcher analogue Phoenix Rod becomes a short range, ammo-efficient flamethrower.
* RandomDrop: Unlike [[VideoGame/{{Doom}} Doom]], where creatures that held ammo would always drop that ammo when killed, the creatures of Heretic would have a varied chance of dropping their particular ammo type, along with some enemies having a particularly uncommon item drop. See RareRandomDrop.
* RareRandomDrop: Some enemies have a rare chance of dropping a valuable artifact instead of ammunition. Notably, the fairly common Disciples of D'Sparil have a rare chance of dropping a valuable [[QuadDamage Tome of Power]].
* {{Retcon}}:
** The protagonist of Heretic was unnamed until Heretic II, which also established that there were a total of seven true Tomes of Power in existence, (At least, his existence, since they reappear in VideoGame/{{Hexen}} II) and that Corvus really had only one of them. The ones he picked up in much larger quantities in his first adventures were fake tomes.
** This seems to be the case with the ending of Episode 3, once [[VideoGame/{{Hexen}} Hexen]] was complete. [[http://static.tvtropes.org/pmwiki/pub/images/heresiarch_heretic.PNG A supposed second serpent rider appears ambiguously angry]] with a crystal ball spying on Corvus after Corvus struck down D'sparil. He wears a serpent rider robe similar to D'Sparil's and D'Sparil himself appears on a stained-glass window in his scrying chamber.\\
This suggests that you would have fought him as a BigBad in another game, but he got DemotedToExtra and became the Heresiarch in [[VideoGame/{{Hexen}} Hexen]]. He summons Dark Bishops to assist exactly like D'Sparil summons his own Disciples of D'Sparil, and instead of TeleportSpam, he uses temporary invincibility.
* SequentialBoss: The final boss uses the same idea: D'Sparil starts out riding a fire-breathing serpent, then after you kill the mount he falls off and starts teleporting around, summoning monsters, and shooting stuff.
* {{Shareware}}: Much like doom, the first episode was shareware.
* ShockAndAwe: The Gauntlets of the Necromancer shoot Green lightning. Powered up, the lightning is red and steals life.
* ShoutOut: The second difficulty level is a reference to Toys-R-Us.
* SnakePeople: The Ophidians; they only appear in the actual "Dome of D'Sparil" and the episodes proceeding the episode of the same name. Their humanoid torsos wear armor plate that covers up their features.
* SophisticatedAsHell: The manual.
* StandardFPSGuns: Even if the weapons are shown as magical staffs, and artifacts, many of them still seem familiar if one has played VideoGame/{{Doom}}. (Shown in terms of WITHOUT / WITH "[[QuadDamage tome of power]]" respectively.)
** Staff = Weak melee attack / [[{{VideoGame/Doom}} Berserker Punch]]
** Gauntlets of the Necromancer = Chainsaw / Short-range LifeDrain Chainsaw
** Elven Wand = Pistol / Rapid-fire Shotgun
** Crossbow = Projectile Shotgun / Projectile Super Shotgun
** Dragon's Claw = HitScan Submachine Gun / Large-Area {{BFG}}-style weapon
** Hell Staff = Energy-projectile Submachine Gun / Area-effect-red-rain
** Phoenix Rod = Rocket Launcher / Flamethrower
** Fire Mace = Short-range gimmick submachine gun / Gimmick {{BFG}}
** Timebomb of the Ancients = Non-throwable grenades (placed in front of the player's point-of-view)
* StoneWall:
** On difficulties less than [[HarderThanHard Black Plague]], the Maulotaur is surprisingly low on aggression, but has 3,000 HitPoints, short of both D'Sparil and his Chaos Serpent at 5,500 hp. Play on HarderThanHard, and Maulotaurs become [[LightningBruiser Lightning Bruisers]] thanks to their "Nightmare!" aggression and their higher chance of using a bull charge.
** The Ophidian only has 280 HitPoints, but is the strongest {{Mook}} in the roster of regular enemies. Their weapon of choice rapid-fires three weak energy balls that cause 1-8 damage each. Then they pause briefly and fire a stronger fireball that causes 3-24. This makes their attacks less damaging than most if you dodge properly and only get hit by one projectile.
* SuspiciousVideoGameGenerosity: Now why would they give you all the items and weapons, along with a full load of big Phoenix Rod orbs, at the start of [=E5M8=]? You'll need them all against the '''''[[OhCrap EIGHT]]''''' ''[[PrecisionFStrike fucking]] [[ThisIsGonnaSuck Maulotaurs]]'' that are ready to kick your ass.
* TookALevelInBadass: Corvus' quarterstaff in the original was the worst weapon you had. Lousy damage, short range, plenty of retaliation time for bad guys, can't harm ghosts at all and any other weapon is better with the Tome of Power. In Heretic II, a blade is added to one end and it becomes one of the coolest weapons in the game that can dismember humanoids to make them harmless, execute spinning attacks or mid-air downward stabs to do increased damage and (with the help of shrines that give permanent upgrades in power) remains a potent weapon throughout the game.
* TornadoMove: The monsters known as Iron Liches can create tornadoes to attack you. The tornadoes sweep you up into the air and do a great deal of damage besides.
** In Heretic II, a powerup finally allows leaving a tornado countermeasure, also in Hexen II the Crusader's third weapon can create tornadoes with the aid of the Tome of Power.
* TragicVillain: Morcalavin. Although his intentions (turning his entire race into immortal [[PhysicalGod physical gods]]) were born of arrogance, and thus not entirely pure, he only failed due to something entirely beyond his control. The Spell of Ascension could only be cast using the seven [[AmplifierArtifact Tomes of Power]]. Unfortunately, Corvus possessed one of them. More unfortunately, Corvus' defeat of D'Sparil ended with him getting exiled to the outer worlds, so Morcalavin had to make do with a duplicate Tome he made himself. This had [[WithGreatPowerComesGreatInsanity unintended]] and [[ThePlague disastrous]] consequences.
* VideoGameFlight: The Wings of Wrath lets you fly for a short amount of time. They return in ''VideoGame/{{Hexen}}''.
* WalkingShirtlessScene: Corvus in ''Heretic II'', who is very fit. At least one reviewer compared him favorably to [[ThirdPersonSeductress Lara]] [[VideoGame/TombRaider Croft]], considering his butt [[FemaleGaze not too unwelcoming to look at]].
* WarpWhistle: The Chaos Device warps you to the beginning of the level. Or, in Death Match, to a random spawn point.
** The Banishment Device from ''Hexen'' does the same thing, except to your enemies.
* WorldHealingWave: Implied at the end of Heretic 2, as the ritual of ascension is complete. It cures the plague but doesn't bring back the dead, as Morcalavin states, "The dead cannot be reborn".