Christian Slater ad-libbed Will Scarlett's line of "Fuck me, he cleared it!", after Robin and Azeem are catapulted over the castle wall. Director Kevin Reynolds kept it in the film, because it was funny, despite the historical inaccuracy.
Rumor has it that Kevin Costner wanted to use an English accent, but Kevin Reynolds didn't want him to. Supposedly, Costner would affect the accent when he was arguing with Reynolds, but not when they were in agreement. Costner claims that he was initially asked to use an accent and hired a dialect coach, but this was stopped (and the coach was fired) when he did it poorly.
Most of the songs the characters sing or hum within the film are actual Medieval melodies. For example, the song Friar Tuck sings is set to the tune of a song called Bacche Bene Venies, from the 13th century Codex Buranus.
Kevin Costner as an American accented Robin Hood, wasn't the only one to not speak in an English accent. When Sean Connery made his cameo as King Richard, he spoke in a Scottish accent. However, Costner had more screen time than Connery and so took more heat for not sounding English, and the real Richard I spoke only Langue d'Oc (a French dialect) anyway.
As Robin, Azeem, and Duncan flee from Marian's, they pull up their horses before entering Sherwood Forest. Kevin Costner's horse half-reared as he halted and the horse's neck came up so fast that it smacked into, and broke, Costner's nose. According to DVD commentary, he did not miss a beat, and continued with the scene.
No mention is made of John, the younger brother of Richard the Lionheart. John was the de facto ruler of England from 1190-1194, while Richard was away fighting in the Third Crusade; however, John did not become de jure King of England until Richard was killed in battle in 1199. In many of the Robin Hood legends, the Sherriff of Nottingham was a loyal follower of John.
The producers, one of them being Kevin Reynolds' longtime friend, Kevin Costner, took over the editing of the film, going to the extent of physically locking the original Editor Peter Boyle out of the editing suite. However, they were contractually obliged, under Directors' Guild rules, to show their cut to Reynolds. He was less than impressed with what they'd done to his film.
Bryan Adams sang a song for this movie "Everything I Do (I Do It For You)",which went on to be the best single of Adams' career, maintaining number one on the U.S. Billboard chart for fourteen weeks. It also spent a record breaking sixteen weeks at number one in the UK.
Robin Wright was the original choice to play Maid Marian, but she had to drop out, as she was pregnant with her first child. The part went instead to Mary Elizabeth Mastrantonio, four days before shooting started. (Wright would land the lead in The Playboys (1992), the following year, because the original actress, Annette Bening, had become pregnant, too.)
Having watched, and been very inspired by the British television series Robin Hood (1984), where a Saracen merry man was introduced into the Robin Hood-legend and let loose in Sherwood Forest, the makers of the film originally called Morgan Freeman's character Nasir, thinking that the character played by Mark Ryan in the British television series was a traditional one, drawn from the old legend. When stuntman Terry Walsh, who had also worked on "Robin of Sherwood" (1984), happened to mention that "Nasir" was not in the original legend, but was completely made-up by the makers of the British television series, the name of Freeman's character was rapidly changed to "Azeem" in order to avoid a possible lawsuit.
In 2012, Kevin Costner sued the producers of the film over unpaid profits. He also alleged that Morgan Creek gave distribution rights to an international subsidiary, which was in breach of its agreement with him.
The film was one of the few Hollywood productions of recent years to receive praise from Jack Shaheen, a longtime Arab-American activist whose book "Reel Bad Arabs" lashed out at all of his perceived examples of motion pictures that contained insulting or inaccurate views of Arabs and Muslims. Shaheen wrote that Morgan Freeman's portrayal of Azeem was very positive, in that Azeem was portrayed as a devout Muslim, and an intelligent, decent man who fights against the vile Sheriff of Nottingham. Shaheen also liked the way Robin Hood indirectly praised the Muslim natives during the Crusades, by saying, "One man defending his home is worth more than ten hired soldiers."
Some of the Sheriff's witty lines (such as telling a couple of wenches "You! My room, 10.30 tonight. You! My room, 10.45. And bring a friend.") were devised by Alan Rickman's friends comedian Ruby Wax and playwright Peter Barnes. He enlisted their help in spicing up his dialogue, because he felt the script was terrible. Kevin Reynolds enabled these script alterations, by not informing the producers or screenwriters, or anyone in the crew. Rickman said in an interview years later, that he knew these new lines were having the desired effect, when during takes, he noticed the crew members covering their mouths trying not to laugh.
The playset that the toy company Kenner made to go with their Robin Hood Prince of Thieves toy line is actually the Ewok village that they made for their Star Wars: Episode VI - Return of the Jedi (1983) line a few years earlier.
A half-hour behind-the-scenes documentary of the film was hosted by Pierce Brosnan, although he did not star in the movie. Sir Sean Connery had played Robin Hood in Robin and Marian (1976), and cameod in this film as King Richard.
In the scene where the Sheirff Of Nottingham is kneeling down in front of a little girl and holding her arms, while speaking to her about having a sad childhood, took a few extra takes. Before the scene was shot, the child actress was introduced to Alan Rickman so she would feel at ease with him. Alan was known to love children and work well with them. So he wouldn't frighten her, he would make silly faces at her and smile while saying his lines. Which caused her to keep giggling during the filming.
The trivia items below may give away important plot points.
The novelization gives insight into a couple of significant edits. First and foremost, Kevin Reynolds was reportedly very upset at the removal of the scene where the Sheriff learns the witch is his mother. Another scene, in which Robin rubs himself with manure, was moved from early in the film to the end. Knowing that this scene was intended to be shown before Robin enters the church explains Marian's request that he "take a bath."
Historical facts: The film's opening scene in Jerusalem in 1194, correctly depicts the city as being controlled by Muslims. Jerusalem had been captured by Salah ad-Din (Saladin) on October 2, 1187. In an early part of the film, the witch Mortianna tells the Sherriff of Nottingham that "the Lionheart returns" from the Third Crusade. The real King Richard did return to England in 1194. At the end of the film, when King Richard appears at the wedding of Robin and Marian, we see the king is wearing a red tabard with three "lions statant" on it. This was indeed the real-life Richard the Lionheart's Royal Arms.