The part of Bishop Edvard Vergérus was written by Ingmar Bergman with Max von Sydow in mind. When the screenplay was completed, von Sydow was contacted about playing the role, which would have been his first in a Bergman film since The Touch (1971). Von Sydow was willing and, in fact, very excited about playing the role. However, Bergman was not aware of this, since von Sydow was in Los Angeles at the time, and could only be reached through his agent who, acting in what he perceived as von Sydow's interest, told Bergman and his producers that von Sydow would only play the role if he could have a percentage of the film's profits, in addition to his salary. The producers, already stretched to their financial limits, of course balked, and told the agent that, sadly, there could be no such compromise, and began looking for other actors to play the pivotal part. By the time von Sydow had learned why his beloved role had been taken from him, Jan Malmsjö had already been cast as the Bishop, and von Sydow lost his chance to star in what would later be known to be Bergman's "last film" (although he would play key roles in The Best Intentions (1992) and Private Confessions (1996), both written by Bergman). Von Sydow was furious about the incident, and, by certain accounts, still harbours a bitter grudge about it to this day.
Famous Swedish song-and-dance man Jan Malmsjö, who is playing the evil bishop Vergerus, thought it was strange that director Ingmar Bergman approached him for a role very much different from anything he had done. He asked Bergman about it, who replied: "Well, I sense some hidden dark and evil streaks inside you, Jan. You have it, I have it, all of us have."
Ingmar Bergman's work diary was released in Sweden in 2006, revealing that the director had intense doubt in his ability to successfully finish the large undertaking that this film presented. There are constant hypochondriacal complaints about illnesses, misery, and fear he might not finish the movie due to personal concerns.
At the end of the film when Emily introduces the idea to Helena that she wants to stage August Strindberg's brand new play "A Dream Play" and that she wishes for Helena to act with her in it, Helena is pretty pessimistic and reluctant about the whole idea and on the mention of Strindberg exclaims: "Oh no... that dreadful woman-hater!". This is somewhat of an in-joke from Bergman towards actress Gunn Wållgren (who portrays grandmother Helena): Gunn Wållgren is first of all well-known as one of Sweden's foremost Strindberg-interpretors ever and secondly; her most successful and praised part on stage was actually the part of Indra's Daughter in "A Dream Play" (a play and a part the actress also loved very much). Gunn Wållgren later in the final scene also recites the first lines of the play's prologue to Alexander.
Although she is an eponymous character, Fanny isn't mentioned in the theatrical version of the film until nearly an hour into its running time. Conversely, in the television version, her name is the first word spoken.
The story takes place during a span of two years from 1907 to 1909. Alexander is supposed to be 10 years old when the events of the film commence. In real life the young actor Bertil Guve was 11 years old. However Alexander has grown and is 12 years old in the final scenes. This means that by the time the production had wrapped after a six month shooting schedule, Bertil Guve was approximately 12 years old coinciding with his character's age.
All three of the Ekdahl sons are named after Swedish kings. In fact, if we assume that the characters are the same age as the actors who played them, then Oscar Ekdahl would have been born during the reign of Oscar I (reigned 1844- 1859), and Carl during the reign of Karl XV (reigned 1859 - 1872). Gustav Adolf would also have been born three years after Oscar, and thus during the reign of Oscar I as well, so he was presumably named after Gustav II Adolph (reigned 1611 - 1632), who made Sweden an international power during the Thirty Years' War, and who is possibly more famous to movie fans as the father of Queen Christina.
Originally, Fanny and Alexander were planned to have a big sister, Amanda, two years older than Alexander, but the character was left out of the film. She does, however, appear in a book based on the screenplay.