When I read that three arrows together are invincible, that's not true. I started doubting, and that's when I started thinking: the house was prosperous and the sons were courageous. What if this fascinating man had bad sons?—Akira Kurosawa, July 1986
Kurosawa first got the idea that would become Ran in the mid-1970s, when he read a parable about the Sengoku-era warlord Mōri Motonari. Motonari was famous for having three sons, all incredibly loyal and talented in their own right. Kurosawa began imagining what would have happened had they been bad. Despite the similarities to Shakespeare's play King Lear, Kurosawa only became aware of the similarities after he had started pre-planning. According to him, the stories of Mōri Motonari and Lear merged in a way he was never fully able to explain. He wrote the script shortly after filming Dersu Uzala in 1975, and then "let it sleep" for seven years. During this time, he painted storyboards of every shot in the film, later published with the screenplay and available as an extra on the Criterion Collection DVD release of the film, and continued searching for funding. Following his success with 1980's Kagemusha, which he sometimes called a "dress rehearsal" for Ran, Kurosawa was finally able to secure backing from French producer Serge Silberman.
Kurosawa once said "Hidetora is me," and there is some evidence in the film that Hidetora serves as a stand-in for Kurosawa. Roger Ebert agrees, arguing that Ran "may be as much about Kurosawa's life as Shakespeare's play." Ran was the final film of Kurosawa's "third period" (1965–1985), a time where he had difficulty securing support for his pictures, and was frequently forced to seek foreign financial backing. While he had directed over twenty films in the first two decades of his career, he directed just four in these two decades. After directing Red Beard (1965), Kurosawa discovered that he was considered old-fashioned and did not work again for almost five years. He also found himself competing against television, which had reduced Japanese film audiences from a high of 1.1 billion in 1958 to under 200 million by 1975. In 1968 he was fired from the 20th Century Fox epic Tora! Tora! Tora! over what he described as creative differences, but others said was a perfectionism that bordered on insanity. Kurosawa tried to start an independent production group with three other directors, but his 1970 film Dodesukaden was a box-office flop and bankrupted the company. Many of his younger rivals boasted that he was finished. A year later, unable to secure any domestic funding and plagued by ill-health, Kurosawa attempted suicide by slashing his wrists. Though he survived, his misfortune would continue to plague him until the late 1980s.
Kurosawa was influenced by the William Shakespeare play King Lear and borrowed elements from it. Both depict an aging warlord who decides to divide up his kingdom among his offspring. Hidetora has three sons — Taro, Jiro, and Saburo who correspond to Lear's daughters Goneril, Regan, and Cordelia. In both, the warlord foolishly banishes anyone who disagrees with him as a matter of pride — in Lear it is the Earl of Kent and Cordelia; in Ran it is Tango and Saburo. The conflict in both is that two of the lord's children ultimately turn against him, while the third supports him, though Hidetora's sons are far more ruthless than Goneril and Regan. Both King Lear and Ran end with the death of the entire family, including the lord.
However, there are some crucial differences between the two. King Lear is a play about undeserved suffering, and Lear himself is at worst a fool. Hidetora, by contrast, has been a cruel warrior for most of his life: a man who ruthlessly murdered men, women, and children to achieve his goals. In the film, Lady Kaede, Lady Sué, and Tsurumaru were all victims of Hidetora. Whereas in King Lear the character of Gloucester had his eyes gouged out by Lear's enemies, in Ran it was Hidetora himself who gave the order to do the same to Tsurumaru. A reviewer notes that Kurosawa had expanded the role of the Fool into a major character (Kyoami), and that Lady Kaede was the equivalent of Shakespeare's Goneril but with a more complex and important character. Kurosawa was also concerned that Shakespeare gave his characters no past, and he wanted to give King Lear a history.