Rumor has it that Kevin Costner wanted to use an English accent, but director 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.
The producers, one of them being director 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.
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 the following year because the original actress, Annette Bening, had become pregnant too.)
The line that Will Scarlett says after he launches Robin and Azeem over the wall, "Fuck me, he cleared it!" is an ad-lib by Christian Slater that director Kevin Reynolds dubbed to "Blind me, he cleared it".
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.
Having watched and been very inspired by the British television series Robin Hood, 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 TV-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.
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 trivia items below may give away important plot points.
The novelization of this movie 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.