Conan the Barbarian

The fantastic Conan short stories from the 1930s by Robert E. Howard were a major source of inspiration for D&D: evil sorcerers, pitch-black dungeons, labyrinthine lost cities, thieves quarters, monsters, the hunt for treasure in ancient ruins. 

There are good sources online for Conan, a Wiki, and a site for d20 conversions. I'm focusing only on the published short stories that were written by REH alone, not on those that were later written, sometimes based on fragments of his.

Conan and D&D

In spite of them being a big inspriration for D&D, D&D is a bad system for creating Conaneseq play experiences, even more so for the more modern "super-heroic" versions of D&D than for OD&D. 

• In D&D, players have access to spellcasting. In the stories, the evil high priest or sorcerer is always the opponent, Conan at best has questionable allies that have some access to it. Sorcery is a sinister force, to be overcome with a clean sword stroke. 
• In D&D, spells are easily used and direct. Most magic in the stories is wrought trough use of magical artefacts or  through alchemical substances, rather than spells. Sorcerers suggest, dominate or mesmerize, or call and control monsters to do their bidding. There are few direct spell effects like fireball or teleport. Instead wizards summon a whirling cloud to fly in, or a winged demon to ride on.  
• In D&D beasts are weak. Most monsters in the stories are essentially dire beasts, with the occasional demon thrown in. Huge, poisonous snakes; sabertooth tigers; gorillas ("grey apes"), and a dinosaur. The latter is called a "dragon" by Conan, but is is just a huge stegosaurus, without treasure, flight, intelligence or fire breath. And these beasts are deadly opponents, it always is a close shave with death if Conan has to fight one, and he generally tries to avoid them.
• D&D has level-based hit points. In Conan there is a scene where he does not dare attack a guard equipped with a crossbow, as he is unarmored and a single hit could kill him. In another a single sling stone knocks him out cold. In fights against beasts, Conan often has one shot at a killing blow to not be crushed to death. In D&D a high level character just can take such attacks, shrug them off, and kill the offender. Conan at the hight of his power is overcome by a dozen common harbor rogues and half a dozen armored city guards are too much for him to fight through. In D&D, a lord could mow down a dozen common men.

Gygax developed D&D stats for Conan himself, and the abilites inelegantly are modeled as mix of fighter and thief (at inflated levels). Later the Barbarian class was created to make this easier. In 5e, Barbarians have a danger sense (though it does not work blind as it does for Conan), but still no stealth. One can fix that with the Criminal background, however, this ability, alongside perception and climibing skills, is depicted to come from barbarian life in the wilderness. 

Runequest, a skill based, non-class based system with fixed hit points, would be a much better fit.

Conan's World

Here is my take on the major kingdoms and empires of Hyperborea, based on the decriptions in the stories. I think the major point to learn here is how by playing on tropes from movies, on stereotypes and on ancient history,  with names that resonate real world cultures, you can convey a lot in little space, and brings people, cities and cultures to live.

He himslelf wrote an essay about the "Hyborean Age", on how these cultures later evolved into the ancient world ones (Egypt, Babylon, the Mongols, Huns, Semites etc.), after the southwest broke of at the Styx/Nile to create Africa, so one can note how the relative neighborhood of these cultures on the map matches those of the European, African and Asian continents, but I think in the stories, he pretty much riffs of of the ancient cultures of earth directly. 

Map credit: GURPS book on Conan, from hyborea.xoth.net

The tech levels of these cultures consequently vary widely from savages to bronze age, to ancient mesoptoamian and hellenistic all the way up to medieval (with chainmail, knights and plate armor). 

Vanaheim, Asgard: Norse myths with giants, so Icelandic, Norwegian, Danish Viking culture. Vanir (Red-haired), Aesir (Blond-haired).

Hyperborea: the home of powerful witches. Cult: Louhi, Bori

Cimmeria: nordic, white, barbarians. Feels close to Germanic tribes. Cult: Crom  

Pictish Wilderness: similar to Scotland, before civilization. Cult: Animistic.

Brythannia: blonde, white skinned folk. Medieval Britain.

Nemedia: Medieval, knightly warfare. He has it as proto-Ireland, I think Germany. Cults: Mitras, Ibis

Aquilonia: Central European Medieval, knightly warfare. Has provinces Potain with Knights that feels a bit like northern Italy, Gunderland with Piketiers and the  Bossonian Marches with Archers that feel a bit like Swizerland and Poland. Could be Aquitaine/Aragon in sourthern France/Northern Spain, but lacks sea access. Cult: Mitras. Capital Tarantina.

Border Kingdoms: No specific country, and I think no stories set there. Could be smaller countries, like Austria, Boehmia, Sowakia etc.

Mediterranean (he has the issue that this sea is missing, instead he has the Vilayet)

Argos: Southern European, Greece or Roman.   

Zingara: Pirates. A feel of Andalusia in Spain, Cordoba and the Barbary coast. Cult: Isthar, Mitra, Bel

Corinthia: Asia Minor like City States. Cult: Anu, Isthar, Bel?

Barachan Isles: Carribean

Middle Eastern

Shem: Olive skin, blue-black beards, hawk noses. Semitic Peoples and Cultures. Think Lebanon, Palestine. Cult: Ishtar, Bel, Set, Pteor, Nergal, Asthoreth. 

Koth: Mesopotamian formerly Archeron, feels assyrian with king Strabonus. Cult: Isthar, Bel, Set. 

Ophir: Shamu sounds mesopotamian, so Babylon (North/South switch with Assyria)? Cult: Isthar, Bel

Zamora: Dark-skinned, dark-haired; thieves, assassins, spies. Mixed Arabs, Scicilians. No coast, normal for a melting pot like this, but explained as on the border between the mesopotamia, steppe and central powers.

Khauran, Kohjara: examples for small kingdoms, like Syria.

Asia

Kozak Steppes: Balkans, Huns. 

Tauran: middle Eastern, Mogul Empire. 

Eastern Desert: Arabia. 

Hyrkania: Mongol Empire.

Kushan: a small Balkan country. 

Iranistan: the name says it all. 

Isles of Pearl: 

Oriental

Meru/Himelians: Himalayah. 

Kithai: China.

Kambuja: Capital Angkor. Cambodja. Cult: Ganesha 

Uttara Kuru:

Vendhya: India.  

Ghulistan: Afghanistan 

Kosala: 

Misty Isles: Spice Islands in the Indian Ocean.

African

Stygia: Tawny folk. Egypt, Cult: Set, Derekto. Capital Luxor, main city Khemri.

Kush: black kingdoms south of Egypt.  

Darfar: black cannibals, filed teeth.

Keshan, Punt, Zembabwei, Black Kingdoms: various black Afrikan kingdoms

Southern Isles: I have less knowledge of African empires, and islands.

Stories

Here are the stories in publication order in synopsis, with the magic, monsters and opponents encountered. Stars are how well I liked them (* least, ***** most).

1. The Phoenix on the Sword****: 8,823 words. Tarantia, capital of Aquilonia. Traitorous nobles & bard, baboon-demon, Toth-Amon, evil sorcerer (dependend on his serpent ring). Serpent ring, magic Sword (endowed by Epemitreus the sage through dream).  
2. The Scarlet Citadel*****: 15,446 words. Aquilonia, Ophir (Plains of Shamu), Koth (Korsemish, the captial, especially Tsotha-Lanthi's dungeons). Treacherous armies of Amalrus of Ophir with Strabonus of Koth, Tsotha-Lanthi the Wizard, eunuch, giant poison snake, gibbering mouther, bottomless pit in darkness, hell-plant, ursurping prince. Ally: Pelias the Wizard. Spells: animate dead, scrying/crystal ball, summon monster (giant demon-bat), polymorph.
3. The Tower of the Elephant****: 9,726 words. Zamora, City of Thieves. Lions, a poisonous giant spider. Yak-Sotha, the imprisioned Elephant God; Yara, evil high priest
4. Black Colossus*****: 14,346 words. Ruins of Kutchemes, Kingdom of Kohjara. Giant poison snake, Natohk's spirit shadow, Natohk's desert nomad army,  polymorphing winged ape demon, Thugra Khotan, 3000-year old evil re-awakened sorcerer-king a.k.a. Natohk the Veiled One,. Spells & Items: Firepowder, morale-boosting spell, sticks to snakes. 
5. The Slithering Shadow***: 12,897. Xuthal, Ruined City in the Deserts of Kush. Opium-drugged citicens, Thalys the Stygian Witch, Thog the shadow demon. Healing potion wine. It feels as if this city (plus Red Nails) inspired B4, The Lost City. Cool story, weak name. (Title turns out to not be Howard's Original. He had named it "Xuthal of the Dusk").
6. The Pool of the Black One***: 11,252 words. Isle of the Black one. Black humanoids. Magical transforming pool with leashing out water tentacle. Sleep poison fruit. 
7. Rogues in the House***: 9,676 words. Corinthia. Rogue, Grey Ape-Man, Nabonidus the Red Priest. Lens systems, Portcullis, ironglass drop-walls & poison dust, no spells.
8. The Frost Giant’s Daughter**: 3,284 words. Vanaheim. Frost Giants, Atali, daughter of Ymir.
9. Iron Shadows in the Moon**: 12,123 words. Vilayet Sea. Lord Shah Amurath, Pirates, Grey Ape, animated iron statues.
10. Queen of the Black Coast**: 11,334 words. Argos, Sea, River Zarkheba. Bêlit the Pirate Queen & Pirates, giant water serpent, black lotus, hyena-weres, winged ape-demon.
11. The Devil in Iron***: 12,292 words. Island of Xapur, City of Khawarizm on the Vilayet Sea. Giant poisonous snake, ironskinned Demon-God Koshatral Kel, Lord Jehungir Agha.  Moonsilver Dagger. Time Magic (restored Ruins, inclusive of inhabitants). 
12. The People of the Black Circle***: 30,890 words. Vendhya (capital Ayodhya, provice Peshkauri), Afghulistan (Khyber pass, Yimsha - the Mountain of the Black Seers in the Himelians). Wazuli tribesman, Khemsa the Wizard, Rakshasas (defeated by destryoing artefact powering them). This is the story with by far the most wizards and spells being slung. Death Curse (using a lock of hair), Cloudkill, Hypnotism/Dominate, Black Ball/Poison Spider, Crimson Cloud (Fly), Hold Person, Polymorph any Object, Wall of Force, Rip out Heart, Polymorph Self; lava and stone block traps; disintegration bubbles, earthquake horn, magic girdle (of spell resistance). 
13. A Witch Shall be Born**: 16,337 words. Khauran. Salome the Witch, Zhaug the Frog-Demon. Crystal of Communication. Too long for the action.
14. Jewels of Gwahlur**: 17,167 words. Keshan, palace of Alkmeenon, forbidden valley. Crushing Stone Trap, Thutmekri the Stygian rogue, Ape-creatures. Feels constructed, with the Jewels lost.
15. Beyond the Black River**: 21,799 words. Pictish Wildernss (Conajohara, Fort Tuscelan & Velitrium). Pictish warriors, sabertooth tiger, giant snake, leopard, panther,  Zogar Sag the Witchdoctor and his swamp devil (a Will'-o-Wisp like demon, half man, half bird).  Shamanistic conjurations and geas/suggestions. 
16. Shadows in Zamboula***: 12,146 words. Zamboula in southern Turan. Cannibals, Baal-Pteor - huge fighter, Totrasmek evil arch priest, Aram-Baksh the Innkeeper. Hypnotic Powers, Illusions. Magical Charming Ring Star of Khorala. Originally called "The man-eaters of Zamboula". 
17. Red Nails*****: 30,946 words. Xuchotl, south of Sukhmet. Dinosaur, Spectral Skull Shaman, citicens of Xuchotl, giant snake, Olmec the prince, bear trap, Tascela the ageless witch, Tolcemek the Adept.  Dominate, Steal Youth; Spectral Skull (similar to Flameskull), Pipes of Madness, Rod of necrotic lightning. This is one of the most influential stories, the maze-like, 4-level plus catacombs city being the poster child for OD&D dungeons with factions and empty rooms. 
18. The Hour of the Dragon***: 72,375 words. Aquilonia, Nemedia, Argos, Zingara, Stygia. Armies of Nemedia, "Child of Darkness" paralyzing Cold-Demon, Soldiers & Jailers, Nemedian Adventurer, Tracking Raven, Nemedian Soldiers, Grey Ape, Executioner, Courtiers, Ghouls, Rogues, Giant Snake, Priest of Set, Vampire, Kithan Monk/Wizard, Xatlotun the Wizard from Archeron, Armies of Nemedia once more. Black pestilence wind, cleansing wind, Earthquake collapsing Cliffs, "Rending the Veil" Scrying past and distant events, Prophecy, Knock, "Black Hand of Seth" (Inflict Wounds?),  Death Dust, Control Weather, Heart of Ariman. The hunt after the heart, wich always narrowly eludes Conan feels forced. Maybe this could have been short story like Scarlet Citadel, if all that had been cut out, and the story had gone directly to overcoming Xaltoun after Conan's escape. Of course, this way we get more fights, shady dealings, world-building and evil sorcery.  Published as "Conan the Conqueror".

REH had chapters around 2,700 to 3,500 words, on average 3,089 words. 

Out of 18 stories, 10 times his main antagonist is some kind of evil sorcerer or evil priest (there is no clear difference in these stories between them), with one more case where the wizard is dead but his minions remain, so nearly two thirds. In the remaining cases, it directly is a demon, god-like creature or supernatural weirdness like the black pool on the island or the statues that animate in moonlight, or the demon Thog (where a witch is thrown in for good measure).  There is no story where it only is "swords" against "swords" of rogues and fighters. It always is swords & sorcery. 

I find it interesting that the publication order of the stories has nothing to do with the timeline in which they happen in-world. Howard starts out with Conan being king of Aquilonia in the first story, (at the end of his career, apparently re-purposing another story) to then goes over his adventures first as a thief, then as a pirate, mercenary and leader of pirates and mercenaries. Here is a scholary discussion of the timeline of Conan stories. 

In brief: 

Conan starts out in Cimmeria, travels into the North (Frost Giants Daughter), attemts to loot a Nemedian treasure house and is caught (God in the Bowl, unpublished), and after that decides to learn how to become a thief, traveling to Zamora (Tower of the Elephant). Eventually he must leave, and travels via neighboring city states (Rogues in the House), finally decides to try something else. This ends his "thief" phase. 

He hires on as a mercenary joining the "Free Companions" that plunder Koth, Zamora and Turan, until they are destroyed by the Turan army under Shah Amurath, whom he slays fleeing to the Vilayet Sea (Shadows in the Moonlight). He wins a pirate ship and crew, loses them again (off screen), and becomes a mercenary for the Hyrkanian army and learns to use a bow, fighting a losing fight against king Yezdigerd of Turan. This ends his phase as a simple mercenary. 

Traveling back west he enlists for the mercenary army of Almaric of Nemedia as a mercenary captain, which supports queen Yasmela of Khoraja, and gets to lead the army against the re-risen sorcerer-king Natohk (Black Colossus). Leaving her service in the resulting peace, he travels to Argos, has a run in with the law and must flee the city by sea. The merchant ship is captured by pirate queen Bêlit, who takes him as her consort and together as pirates they plunder the coast, until she and the crew perish in an expedition to the lost city of Zarkheba (Queen of the Black Coast). 

He leaves hires again with Almaric, who is fighting a rebel war against King Strabonus of Koth. As the rebels are destroyed by the Stygian black plage, Conan flees into the southern desert, where he encounters the forgotten city of Xuthal (Xuthal of the Dusk). He returns North via Darfar and Lake Zuad, and hires as a captain of the guard in Khauran (A Witch Shall be Born). After saving the queen, he remains a leader of Zuagir raiders, plundering Shemitish City-States and Turanian outposts, until Turan fields an army against them. He moves North, joining the kozaki bandits and working his way up through the ranks there until he becomes the hetman of the kozaki. Making an alliance with the pirates of the Vilayet, he continues plundering Turan, who set an unsuccessful trap for him (The Devil in Iron). Finally the spy Kerim Shah manages to betray him and have his troups are destroyed (of screen).

Conan moves on to Afghulistan, where he becomes a war chief of the Afghuil hill tribes, plundering Turan and Vedhya. Yedzigerd of Turan enlists an archwizard to kill the king of Vendhya and Conan helps Vendhyas devi Yasmina to take revenge (People of the Black Circle), and realizes the hill tribes cannot challenge these strong empires. He travels to Zamboula, where he squanders his wealth (Shadows in Zamboula), and flees the city with a sack of gold and a magical ring which he hopes to sell to the queen of Ophir.  

Some unpublished adventures later as a Barachan pirate plundering Argos, Zingara, and Stygia, he escapes a trap in Tortage in a leaky rowboat and joins Zingaran freebooters, taking over ship and girl (Pool of the Black Ones), until a storm destroys all. 

A wanted man in Argos, Stygia, Zingara, and Turan, he travels to Aquilonia and hires with the military at the Pictish border (Beyond the Black River). After other adventures, he rejoins the "Free Companions", and meets Valeria, whom he follows to the lost city of Xuchotl (Red Nails) and the Black Coast, Valeria returning to the sea. Conan travels to Keshan, to steal fabled juwels (Jewels of Gwahlur), but fails. 

He returns to Aquilonia, and there he raises quickly through the army ranks and leads a regiment of mercenaries. After defeating an invading Zingaran army together with the knights of Potain, count Trocero of Potain challenges king Namedides's rule and supports Conan's bid for the throne. Together they defeat the army of Namedides, March on Tarantia, and, at age 40, Conans strangles Namedides on the Throne to become king. Thus ends the long an varied phase of being a leader of mercenaries and pirates. 

Now Conan is king of Aquilonia. He survives an assassination attempt by dissenting nobles (The Phoenix and the Sword), then is betrayed by Ophir and captured (The Scarlet Citadel), but escapes and returns in time to save his kingdom. He again is captured and defeated through black magic by an ancient sorcerer raised from the dead, and his kindom is conquered, but he but escapes with the help of the seraglio girl Zenobia, wins it back and makes her his queen (The Hour of the Dragon). Here the stories of Conan end.