All of the characters except Rodney Skinner (the Invisible Man) have fallen into the public domain, which means that anybody can write about them. Apart from the 19th Century characters used in the film, this goes for some Golden Age comic book characters.
When Alan Quartermain is teaching Tom Sawyer to fire long-distance shots, you can see Shane West's (Tom Sawyer) arm and shoulder shaking from the strain of holding the gun. He says on the cast commentary that he was quite embarrassed because Sean Connery, who was nearly 72, seemed to have no problem holding the solid wood and metal gun while firing a shot, whereas he, in his early twenties, found it incredibly heavy and strained to hold it still while aiming at the target.
At one point, Peta Wilson does a humorous impersonation of Sean Connery's voice. According to Wilson, this was a last-minute addition to the scene, and she felt nervous doing it, since Connery impersonations was considered a no-no on the set. Before the shoot she called Connery and offered not to do the accent, but he insisted she should. Afterwards she asked him what he thought. He replied, "You were great!" She was taken aback and asked if he really meant it. He said, "Yeah, it's terrible! It's the worst impersonation I have ever heard, and it's perfect."
The reason Captain Nemo denounces the kidnapping of the scientists' wives and children as 'monstrous' is from personal experience. In Jules Verne's original story, Nemo's own wife and child were kidnapped and murdered; grief-stricken, Nemo built his submarine and retreated into the sea.
While filming in Prague, the cast went to an Indian restaurant for lunch. The Indian proprietor recognized Naseeruddin Shah, called him by name, escorted the party to his best table, and waited on them personally.
While capturing Hyde in Paris, Quartermain says Hyde has been terrorizing the Rue Morgue for some time. An allusion Edgar Allan Poe's "The Murders in the Rue Morgue", another famous 19th-century literary work.
In the original graphic novel Alan Quatermain had written himself out of public life and become an opium addict. At the start of the story he is rescued from a Cairo opium den by Mina Harker and enlisted as a member of the League. In the film adaptation, Sean Connery reportedly refused to play an opium addict, so the writers changed his story so he was merely hiding from the public, and still in control of his wits and health.
Fox was unable to get the rights for the literary character of The Invisible Man created by H.G. Wells. Not only did this necessitate the character in the film have his name changed from the book's "Griffin", but that he could never be referred to as "the" Invisible Man, only "an" invisible man.
Tony Curran's agent did not want him to take the role of Skinner. He reasoned that since the character is invisible for most of the film, no one would care about who was playing him. Once the film came out Skinner became a fan favorite.
LXG takes place in an alternate universe where technology is more advanced in 1899 than it was in real life. Aside from the use of an automobile and other advanced devices, we also see Captain Nemo's crew using sonar and Nemo refers to solar power many years before they were invented.
In the comic book version of The League, Mina Harker (who refers to herself by her maiden name, Mina Murray) does not have vampiric abilities. The only reference to her past are large scars from bite marks on her neck which are hidden by a scarf. Additionally, she is the League's leader, the one who is responsible for recruiting the other members.
A sequel was planned but was canceled due to negative critical reception and the film being a grave disappointment at the box office. A clue to the sequel's plot can be gleaned from a poster in the background which says "Volcanic eruptions on Mars". This would of been an adaptation of the second series of the comic book, where the League battled the Martian Tripods from H.G. Wells' "War of the Worlds".
Two portraits in the meeting room represent previous Leagues. The first shows Robin Hood (from various legends/poems), Ivanhoe (from Sir Walter Scott's novel) and the Black Arrow (a Robert Louis Stevenson novel). The Black Arrow, though, is set in the 15th century (during the War of the Roses), far later than Robin Hood and Ivanhoe, but this may be one of the many who took the name prior to the novel's setting. The other portrait displays the Four Musketeers - Porthos, Athos, Aramis, and D'Artagnan (from the various novels by Alexandre Dumas père), the Sea Hawk and Captain Blood (both pirates created by Rafael Sabatini and, incidentally, both played by Errol Flynn in the movies). These are according to the screenplay of the film.
When the League arrives at the London Docks, the camera passes by a wall with a poster for a carnival that is coming, there are two names: Dr. Alan Moore and Dr. Kevin O'Neill. These are the names of the gentlemen that created and wrote the comic "League Of Extraordinary Gentlemen". The poster is, in fact, a duplication of the title page of the League of Extraordinary Gentlemen Vol. 1 collected edition.
A scene was cut from the film where Tom Sawyer explains that he and his friend, Agent Huck Finn, were tracking down the Fantom, and that the Fantom killed Huck. This is the reason why Sawyer is so intent on getting the Fantom.
During the battle of Venice, there is a brief shot of the footwell of the NemoMobile. Shown are three pedals, however, Tom Sawyer slams his foot on the gas pedal without ever touching the clutch. This is because, a) The NemoMobile used an automatic transmission and, b) the pedal on the far left is in fact, not a clutch pedal, but rather a second brake pedal. By having independent braking to the left and right side of the car, the stunt driver could achieve certain tricks not normally attributable to a 22 foot long vehicle.
Although Alan Moore uses "Quatermain", and this is often considered the canonical spelling of the character's name, H. Rider Haggard himself occasionally used "Quartermain", and that spelling is used several times throughout the movie (especially obviously on the grave marker).
The character of Campion Bond, British Intelligence director (ancestor of James Bond), was supposed to appear (one media report suggested that he would be played by Roger Moore, thereby having two former James Bonds in one movie), but the character was dropped before filming began to be saved for a possible sequel, which was never made.
The film's creators were sued in 2003 by Martin Poll and Larry Cohen. Poll and Cohen claimed that they had pitched a similar idea to Fox between 1993 and 1996, under the title 'Cast of Characters'. They alleged that Fox hired screenwriters to adapt Alan Moore's comic long before it was finished, and instead used ideas from their screenplay to make up the story. The case was settled out of court.
A portrait seen in the background of one shot appears to be of a previous League, and corresponds to a similar portrait seen in the comic. This previous (1780s?) League consists, then, of: The Reverend Dr. Syn (created by Russell Thorndike), pirate and highwayman; Sir Percy Blakeney, the Scarlet Pimpernel (created by Baroness Orczy); Natty Bumppo/Hawkeye/Deerslayer/Leatherstocking, hero of "Last of the Mohicans" by James Fenimore Cooper); and Lemuel Gulliver, of "Gulliver's Travels" by Jonathan Swift). Two female members appearing in the comic portrait - Lady Blakeney (from the Scarlet Pimpernel) and Fanny Hill (created by John Cleland) - are absent.
According to producer Don Murphy in a making-of featurette on the DVD release, pre-production work on this film actually predated the publication of the first issue of the comic book. This may explain why there are noticeable differences between the film and the graphic novel.
There were widespread rumors that Jason Isaacs was to play the part of British Agent Campion Bond. However, in an interview Isaacs revealed he hadn't even read the script and that all reports of him in the role were, in fact, fabricated.
Production delays and constant clashes between himself and director Stephen Norrington convinced Sean Connery that he had fallen out of love with modern film making. While he made no official announcement at the time, he has since insisted that he is now officially retired, save for some voice-over work.
The addition of Tom Sawyer to the cast may have been meant to increase the movies appeal to US audiences but it wasn't just a whim. After 'The Adventures of Huckleberry Finn''s success, Mark Twain wrote little-known two sequels to "Tom Sawyer" in one of which Tom has a Jules Verne-like adventure ('Tom Sawyer Abroad') and in the other, becomes a detective ('Tom Sawyer, Detective').
The biggest change between the comic and the film version is the relative downsizing of Mina Harker and Nemo. In the film, Sean Connery is the leader and protagonist, along with the American Tom Sawyer. The comic had the lady, Mina, as the undisputed leader and Nemo was responsible for many decisions. A significant part of the action was led by Mina and Nemo. This change missed the whole point of the comic, and contributed in part to it's abysmal failure.
Three clips from the original script, also featured in the novelization, are shown in the UK trailer. The first is Nemo, Jekyll and Skinner on the conning tower of the Nautilus. The second shows Eva Draper, a character completely cut from the film, just before Sawyer saves Quatermain's life in M's fortress chamber. The third is when Quatermain chases the Phantom through Venice, and tackles some of his henchmen on a boat. These are all brief, but clearly seen.
Actor Richard Roxburgh later referred to the finished film as "an unadulterated stinker". He had signed onto the project as an opportunity to work with Sean Connery and Stephen Norrington. Roxburgh said that he realized too late that the film was going to be a bad experience when he arrived on set during the first day. However, Roxburgh did praise the graphic novel.
The trivia items below may give away important plot points.
The film's literary characters are Allan Quatermain, introduced in H. Rider Haggard's "King Solomon's Mines" (1885); Mina Harker from Bram Stoker's "Dracula" (1897); Henry Jekyll and Edward Hyde from Robert Louis Stevenson's "The Strange Case of Dr. Jekyll and Mr. Hyde" (1886); Rodney Skinner, who replaced Griffin from H.G. Wells' "The Invisible Man" (1897) (due to rights issues, and the character in the comic was given the name Hawley Griffin as the original novel gave no first name); Captain Nemo from Jules Verne's "20,000 Leagues Under the Sea" (1870) and "The Mysterious Island" (1874); Dorian Gray from Oscar Wilde's "The Picture Of Dorian Gray" (1891); Tom Sawyer from Mark Twain's "The Adventures of Tom Sawyer" (1876) and its sequels; Ishmael from Herman Melville's "Moby Dick" (1851); and Professor James Moriarty from Sir Arthur Conan Doyle's "The Final Problem" (1893), one of the Sherlock Holmes stories. The Fantom's mask design alludes to Gaston Leroux's "The Phantom Of The Opera" (1911). British Intelligence chief "M" alludes to "Casino Royale" (1953) by Ian Fleming as does Campion Bond, a character from the script (who never made it into the movie), who is supposed to be the grandfather of James Bond.
Allan Quatermain, Nemo, Jekyll & Hyde, Dorian Gray, and Professor Moriarty all died in their original novels or stories. In the novel "The Invisible Man" Dr. Griffin went quite mad and was eventually killed. Here, Skinner says he got the serum to turn himself invisible from a mad doctor, a very clever way to get around the rights issues. Both the original Invisible Man, Mr. Hyde, and Nemo were far from heroes in their original incarnations. Nemo was a rebel to the crown and Mr. Hyde and the Invisible Man were murderers and rapists.
In the fight scene in Dorian Gray's library with the Fantom. When the Fantom flees and runs out chased by Quartermain one of the Fantom's henchmen jumps down to stop Quartermain's chase. As he does this he yells "Run James." Giving a clue to the Fantom's real identity that of Professor James Moriarty, enemy of Sherlock Holmes.
Stuart Townsend stated in an interview that he was the only one of the seven League members whose contract did not bind him to a three-picture deal. He said they were going to ask it of him, but he observed that it would be pointless since his character is killed in the movie, and they agreed to contract him for only one picture.
When Quatermain first enters the downstairs meeting room at the headquarters for the League we can see Masonic symbols carved on the face of the door. The same symbol appears on the Fantom's ring, foreshadowing the Fantom's true identity.
In the original script, it is revealed at the end that Skinner is actually an agent for British Intelligence. He was working undercover to see if Sanderson Reed was actually a double-agent working for the Fantom.
After confronting M in his fortress vast, Quartermain calls him James Moriarty, the archenemy of Sherlock Holmes. As he escapes from Quartermain and Sawyer, Moriarty throws a knife at Quartermain which impales a portrait of Napoleon. Moriarty's most famous nickname is The Napoleon of Crime.