10. Barbara Gordon is Alfred's niece (Batman & Robin)

In the much-reviled fourth instalment of the 1989-1997 Batman film series (and fifteenth highest-grossing film of 1997 according to Box Office Mojo, fourteenth if the rerelease of Star Wars Episode IV: A New Hope doesn't count), Alicia Silverstone played Alfred Pennyworth's niece Barbara Wilson, who would later become Batgirl in the climax of the film. Sad to say that this film derailed Silverstone's career.

Blonde-haired Barbara Wilson is based on red-haired Barbara Gordon. However in the comics, Barbara Gordon is not related to Alfred at all and is Commissioner Gordon's daughter (or niece / adopted daughter in some versions). 

9. Dick Grayson has an older brother (Batman Forever)

In the much-polarised Batman Forever, Dick Grayson oversees the deaths of his parents and older brother. In the comics, he was ten-to-twelve years old when he saw their deaths but in the film, he was a young adult. 

Grayson has an older brother in the third instalment named Mitchell, but in the comics, he doesn't as he has younger adopted brothers (he is Bruce Wayne's adopted son after all), which are Jason Todd, Tim Drake and Damian Wayne, all of them became Robin after he became Nightwing.

8. Lois knows about Superman's secret identity (Man of Steel)

In the controversial, but successful Man of Steel film, reporter Lois Lane is wounded before Clark Kent saves her. During the film, she writes a story of how she was rescued by a superhuman (referring to Clark), but is rejected by The Daily Planet editor Perry White. She promises not to reveal Clark's secret after hearing his story. In the end of the film, she pretends not to recognise him when he takes up a journalist job at The Daily Planet.

In the comics, Lois wouldn't know that Superman and Clark Kent were the same person until the fateful issue that was Action Comics #662 when after proposing to her, Clark told her he was Superman. Because of this, they would remain a couple until Dan DiDio decided to show true art is angsty by rebooting the Post-Crisis continuity into the New 52. 

7. Constantine is American (Constantine)

Remember in 2005 when John Constantine had his first live-action appearance in Constantine (one of the five film adaptations of works by Alan Moore in which Moore has publicly disowned). Here, he is a raven-haired, brown-eyed American chain smoking occult detective played by Canadian actor Keanu Reeves, who is of mixed Native Hawaiian/English/Chinese/Portuguese descent.

In the comics however, he is a blond-haired, blue-eyed Brit whose appearance was based on British singer and The Police lead singer Sting. Eventually, Welsh actor Matt Ryan got the appearance from the comics right for the NBC TV series, also called Constantine.

6. Patience Phillips is Catwoman (Catwoman)

In the much-reviled "in name only" film adaptation of Catwoman, Halle Berry plays graphics designer Patience Phillips, who is apparently drowned after witnessing that the Beau-Line aging cream has a side effect, before being mysteriously resurrected by an Egyptian Mau cat, thus resulting her to become the vigilante Catwoman.

In the comics, the Patience Phillips incarnation of Catwoman doesn't exist and there has been two women who took over the Catwoman mantle from Selina Kyle: lesbian sidekick and fellow friend Holly Robinson (when Selina became a mother to a daughter named Helena, nod to the daughter of Catwoman and Batman of Earth-Two) and Japanese American Yakuza heiress Eiko Hasigawa (when Selina became a mob boss and then kissed her in Catwoman vol. 4 #39).

5. Henri Ducard is Ra's al Ghul (Batman Begins)

In the first instalment of the critically acclaimed and commercially successful Dark Knight Saga, Bruce Wayne's mentor at Bhutan, Henri Ducard is revealed to be the leader of the League of Shadows and the main antagonist Ra's al Ghul in a plot twist that leads to the climax.

In the comics, they're two different people. In fact, Ducard was created by Batman 1989 writer Sam Hamm, while Ra's real name has never been revealed.

4. Superman has a son (Superman Returns)

In the much-polarised, yet overlooked retcon sequel to Superman and Superman II, Lois Lane's son with fiance Richard White (Perry's son), Jason is revealed to be Superman's son when he displays superhuman strength as he throws a piano at one of Lex Luthor's henchmen, killing him. 

In the post-Crisis comics, Superman has an adopted son named Chris Kent, who is actually Lor-Zod, the son of his second arch-rival (first is Lex Luthor) General Zod. He briefly donned the Nightwing mantle when Dick Grayson became the new Batman. In the possible future of the New 52, it's revealed he has a son with Lois Lane named Jon Lane Kent, who goes to the present to usurp the Superboy name and is responsible for the apparent death of Kon-El (though he was later revealed to be alive in the conclusion of Superboy volume 6).

3. Superman confronts an evil counterpart of him (Superman IV: The Quest for Peace) 

In the franchise-killing fourth instalment of the 1978-1987 Superman films, Lex Luthor uses a strand of Superman's hair to create his own superhuman, which is the Nuclear Man, who kicks Superman into the distance.

Superman has two evil counterparts in the comics, Hank Henshaw aka Cyborg Superman and Bizarro. Nuclear Man (not Firestorm the Nuclear Man) never appeared in the main comics.

2. John Blake is Robin (The Dark Knight Rises)

In the end of the critically-acclaimed, commercially-successful but fan-polarised conclusion to the Dark Knight Saga, John Blake tries to retrieve something for him from the estate of Bruce Wayne, but fails to do so until he shows a female clerk his full name in his card: "Robin John Blake". Despite Christopher Nolan's statements that Robin would never appear in his trilogy, it was the closest thing of ever happening.

John Blake is a composite character of all three Robins: He's a cop like Dick Grayson, he was an orphan and had street smarts like Jason and he realised that Bruce Wayne and Batman are the same person like Tim. Plus, him inheriting the Batcave is a nod to Terry McGinnis.

1. The Joker killed Thomas and Martha Wayne (Batman)

During the flashbacks for the first instalment of the 1989-1997 Batman film series, hitman Jack Napier kills Bruce Wayne's parents Thomas and Martha in cold blood. Around thirty years later, he's the main antagonist the Joker.

In the comics, Joe Chill is the one who killed Batman's parents, while the Joker's real name has never been revealed. In fact, Tim Burton's idea of the Joker being the killer of Batman's parents was approved by Bob Kane himself, who said that he would've done it in the comics had he introduced the Joker at around the same time he had created Batman.