Marlene Dietrich turned down the rule of Raina Arkadin.
Maurice Bessy ghost wrote the Mr. Arkadin novel that was released shortly after the movie premiered. Though Orson Welles is credited as the author, Welles didn't write a single word of it.
Mr. Arkadin was created from three episodes of the 1951-1952 radio program, The Lives of Harry Lime: Man of Mystery (AKA Greek Meets Greek), Murder on the Rivera and Blackmail Is an Ugly Word. Arakdin is based mostly on the first of the three and centered on a character named Gregory Arkadian. Primary characters and set-ups are taken from the other two episodes.
The credits read "And introducing Paola Mori". However, she had been in at least four films prior to this. The credits also imply the "And introducing" refers to Robert Arden as well, who also had had at least two credited big screen performances.
The novel and the screenplay were both based on an episode in the radio series, "The Lives of Harry Lime", in which Welles played his Harry Lime character as rather less villainous that he was in The Third Man. In "Mr. Arkadin", the Harry Lime character is renamed "Guy van Stratten" and is played by Robert Arden, while Welles plays Arkadin. The radio episode was number 37 in the series, entitled "Man of Mystery," and first broadcast on 11 April 1952. The introduction to the episode also describes the movie: "One late afternoon a couple of years ago, a plane was sighted about seventy miles out of Orly Airport in Paris. It was a private plane, medium sized, and nobody was in it; nobody at all. The plane, keeping its course steadily toward Paris, was flying itself. Why was it empty? Who had been flying it? And why, and under what circumstances, had they left it? Why? Thereby hangs a tale."
Until recently, the version in possession of Corinth Films was generally regarded closest to Orson Welles's cut. In April of 2006, the Criterion Collection released a comprehensive three-DVD set of the film, featuring three versions: the "Corinth" version, "Confidential Report" (the European cut), and the newly edited "Comprehensive" version. Each version contains a few shots or lines that are missing from the other two. Because the film was taken out of Welles' control in post-production, we will never know exactly what he had in mind for the complex flashback structure he spoke of later in his life.