The Friedrich Nietzsche quotation that opens the movie, "That which does not kill us makes us stronger", is a loose translation of "Was mich nicht umbringt, macht mich stärker", which more properly translates as "That which does not kill me, makes me stronger." It's from "Twilight of the Idols", Maxims and Arrows, 8.
In an interview, John Milius said that the dogs they used in the film were very unfriendly and dangerous. He even went as far to say "When you had the dogs chasing Arnold Schwarzenegger and he's running, he's actually running for his life because he knew those dogs were very dangerous and they even attacked their trainer".
Arnold Schwarzenegger had weapons training, martial arts training, and horse riding lessons from specialists. He trained with an 11-pound broadsword two hours a day for three months, and learned how to handle one; each broadsword cost $10,000 and had to look weathered. He also learned climbing techniques, and how to fall and roll and jump at least 15-feet in the air. John Milius made sure all of these were videotaped, and according to Schwarzenegger, they were just as intense as training for bodybuilding competitions. Franco Columbu was his trainer and was rewarded with a small part in the film.
James Earl Jones was a last minute addition to the cast because of his commitments on Broadway. He and Arnold Schwarzenegger became friends on-set; Schwarzenegger helped Jones stay in shape and Jones coached Schwarzenegger on acting; so did Max von Sydow.
The fake blood used in the film came in the form of a concentrate, which had to be mixed with water prior to use. Due to the cold weather, it was mixed with vodka (as an anti-freeze) instead. In the scenes in which the actors were supposed to spit the blood, they would swallow it instead, then go back to the special effects man for more.
Although Conan and Valeria are shown together frequently throughout the movie, he only speaks five words to her in the entire film - and they're all in the first thirty seconds after they meet: "You're not a guard", and "No".
When Oliver Stone wrote the script, he made Arnold Schwarzenegger read comics and fantasy novels to see how he handled period dialogue. Stone set the story in the future after the downfall of civilization; it was to be a four hour saga and had a whole host of creatures. It would have cost the studio 70 million dollars to pull that off so they refused. John Milius wound up rewriting much of Stone's script, which cut the budget by more than half, which also called for a change in location. He wanted the fantasy accurate in every detail.
Conan's response to the Mongol General is an abbreviation of a real quote attributed to Genghis Khan: "The greatest pleasure is to vanquish your enemies and chase them before you, to rob them of their wealth and see those dear to them bathed in tears, to ride their horses and clasp to your bosom their wives and daughters." Subotai (or Subedei Baghadur) was the name of Great Khan's general. The fact that Conan is not only chased but to some extent orphaned by dogs also recalls Genghis Khan's well-documented fear of that particular animal. Finally, the writers' preoccupation with steel seems oddly coincidental, given that Genghis Khan's birth name, Temujin, is frequently translated as "finest steel."
A Conan expert was brought in to tutor Arnold Schwarzenegger on how to live like the character, e.g. sleeping outdoors, living off the land, etc. Schwarzenegger thanked him by getting him cast as an enemy warrior hacked to bits by Conan. He was delighted that Schwarzenegger had been cast as Conan, as were the fans.
There is an enduring urban legend about the so-called "Conan toy line". The story is that the Mattel Toy Company started to make some Conan action figures, but after viewing the film, the executives realized that they couldn't afford to be associated with a film with such graphic sex and violence. They gave their doll blonde hair, called him "He-man", and thus created He-Man and the Masters of the Universe (1983). However, since the first He-Man figures were released in 1981, the legend appears to be false. In 1984, however, now-defunct toy company Remco released an officially licensed series of Conan action figures. Ironically enough, once the He-Man action figures became immensely popular, numerous knockoffs were produced, including a repainted He-Man figure that had brown hair, making it look like Arnold Schwarzenegger. The knockoff was sold mainly through mom-and-pop dollar stores and came in generic packaging labeled "The Barbarian".
Arnold Schwarzenegger had retired from professional bodybuilding after winning the 1975 Mr. Olympia contest. He got back into such good shape while training for his role in "Conan the Barbarian" that he decided to enter the 1980 Mr. Olympia contest. He won the contest although there was a great deal of controversy about whether he deserved the victory.
Director John Milius says in the documentary Frazetta: Painting with Fire (2003) that more than a few scenes were dedicated to legendary artist Frank Frazetta and based on his artwork, including the scene in the orgy chamber, Thulsa Doom turning into a snake, a girl chained to a pillar and a climactic fight scene.
Arnold Schwarzenegger suffered a back injury (among other various assorted injuries) while filming when the dogs who were chasing him jumped him from behind and he fell down the rock he was climbing to escape them.
The snake cult of Thulsa Doom is modeled after the Flagellants-a cult that arose in Germany at the time of the Plague of the Black Death in the mid 14th. Century. They are wearing similar white robes and some are whipping themselves.
200 workers built the sets in a large warehouse outside Madrid. The production crew were made up of people from Italy, England, the US and Spain. 1500 extras were employed and the score was performed by a 90-piece orchestra and a 24-member choir, singing mock Latin.
Although the "Hyborian Age" of Conan was approximately 10,000 BC, creator Robert E. Howard used Medieval themes and influences in the Conan stories to avoid any complicated historical research. Oliver Stone's script placed the story in a post-apocalyptic future rather than the distant past. This was abandoned and the original timeline was restored.
According to producer Raffaella De Laurentiis, pre-production for the movie initially began in Yugoslavia, but due to the political instability in the area, it was ultimately decided to move the rest of the movie's production to Spain.
Due to production delays, Arnold Schwarzenegger took smaller supporting roles in the interim to give him more experience in front of the camera. During filming, he was away from Maria Shriver for five months, so she tried visiting the set as much as she could.
Universal were worried the film's violence was too excessive for viewers. Sid Sheinberg, the president of Universal saw a rough cut and thought it too violent for a holiday release so it was pushed back. On Golden Pond (1981) was Universal's Christmas release instead. The censors asked John Milius to tone the violence down which he did, but in the end it still wasn't enough for them. Arnold Schwarzenegger was annoyed about that but now thinks it brought more people to see it; it was his first real taste of large scale studio marketing and he also helped promote the film in six different countries.
The script called for Conan to throw a torch into the palace's central window/balcony. Arnold Schwarzenegger missed on the first attempt, but no retake was possible as the set proceeded to burn to the ground, as intended.
Arnold Schwarzenegger said in the behind the scenes features that during the crucifixion scene, they used a live vulture to peck at his wounds. Then for the close up they used a real dead vulture they found for him to actually bite into its throat. After they cut, they immediately had Arnold rinse his mouth out to avoid disease.
The scene of the crucifixion on the dead tree was shot in Almeria, Spain. When Conan is nursed back to health, we can see mysterious magical figures drawn all over his face. One of them is the "indalo" (a red symbol resembling a man with his arms over his head), a traditional symbol of the province of Almería used since ancient times by the local inhabitants to expel witches and lightning. Now it has become a symbol and tourist trademark icon for the province and its tourism industry.
The life of Conan oddly mirrors that of Arnold Schwarzenegger. Conan's formative years are spent in a small village, then spent in hard manual labor as a slave. Then Conan gains fame and wealth through his physical prowess. Although at first given to wine and women, he eventually abandons his hedonism and uses his skills for acts of heroism. Eventually, Conan becomes a king. In real life, Schwarzenegger was born in a small Austrian village and spent his life bodybuilding. He then becomes famous and wealthy through bodybuilding competitions and action/adventure movies. Schwarzenegger engaged in drug use and womanizing in his past, but gave those up later in life and then campaigned for social causes. Eventually, he was elected Governor of California.