Marty McFly is an iconic character in the sci-fi scene, but the face we all know and love today may have been a different one, as Michael J. Fox initially wasn't available for the filming due to conflicting schedule, so the role was given to Eric Stoltz. Sid Sheinberg, head of Universal, even supported this casting. Despite filming most of his scenes, Stoltz was deemed to be too dramatic and lacking the humorous flair imagined for the role, so Fox was contacted again and the scheduling conflict was worked out. Zemeckis took it upon himself to inform Stoltz of the decision and later said it was “the hardest meeting I've ever had in my life and it was all my fault. I broke his heart."

Beverly Hills Cop is considered a comedy classic, but when Sylvester Stallone was cast as Axel Foley, he wanted to shift the script to be include more heroics for his character, turning Alex into a certified action figure. Such a take on the film was rejected and Stallone was replaced by Eddie Murphy, who gave the film his unique charm.

Stuart Townsend, a relatively new name in the industry, was cast as Aragorn in Lord of the Rings, but when the filming began, he lasted only a few days. The director was quick to notice Townsend was too young to play the Strider, and the role was given to Viggo Mortenson, who gave an iconic performance.

Nicole Kidman had already begun filming for the role of the distressed mother in the thriller Panic Room when she injured her knee. Unfortunately, she had previously injured the same spot while filming Moulin Rouge and now had a hairline fracture which left her unable to continue filming. The role was given to Jodie Foster, who had to shut down the movie she was about to direct because the star, Russell Crowe, was injured.

Love him or hate him, we all know who Wolverine from the X-Men is, as well as the actor who plays him. But the role of the gruff hero was intended for Dougray Scott, who, back in 1999, was making quite a name for himself. However, Scott's other project dragged on and he wasn't available when the X-Men started filming, thus the role was given to Hugh Jackman and the rest is history.

The Truman Show is a very impactful movie with plenty of deep themes and ideas, and what made it half as good is the actors. The role of Christof, the mastermind behind the fake town, was initially given to Dennis Hopper; however, there were difficulties with his portrayal (with a possible allegation of forgetting his lines), and so the role was then assigned to Ed Harris, who excelled at it!

Oscar nominee Annette Bening was originally cast as the Catwoman, quite a prominent figure in Batman's life. However, Bening had to leave the production once due to pregnancy, and Michelle Pfeiffer stepped up to fill in her shoes. The change was unexpected, and Pfeiffer was even said to have worn outfits measured for her predecessor because of the rush to start filming.

Back in the '90s, Lori Petty was making a name for herself as a reliable actress, and was set to appear in Demolition Man together with big names like Sylvester Stallone and Wesley Snipes. However, she reportedly didn't get along with Stallone, and was replaced by a relative newcomer in the industry—Sandra Bullock.

The fans of the Alien franchise likely all recognize the face of Michael Biehn, who played Hicks, but this role didn't land in his lap initially. At first, the character was meant to be played by James Remar, but he was fired after a few weeks of filming due to creative differences. Later, the actor himself admitted he had a drug problem and lost the role because he was in possession of drugs.

The iconic character from V for Vendetta may have had different mannerisms if the director had decided to go with his first pick for the role. James Purefoy inhabited the character of V for a whole 6 weeks of filming before it was decided he couldn't properly emote while wearing a mask. Hugo Weaving was asked to take over as V, and it's his portrayal that we see in the movie.

Predator in Predator may be recognizable by its look, not the actor behind it, but there was a chance Jean-Claude Van Damme could have embodied the feared hunter. However, apparently the prosthetics and the costume were so stifling, the actor even passed out wearing them. The real reason why Van Damme left the project is a bit of a mystery, but his place was taken by Kevin Peter Hall.

Some recasts have to be done out of great necessity. Such is the case with All the Money in the World, where Kevin Spacey was initially supposed to play the role of an oil tycoon. Due to sexual assault allegations involving him, the director Ridley Scott quickly removed him from the movie, reshooting all his scenes with Christopher Plummer, who even received an nomination for an Academy Award.

Harvey Keitel was hired to play the role of captain Benjamin L. Willard in Apocalypse Now, despite not being the director's first choice. However, his portrayal lacked the passive feeling that director envisioned, so the role was offered to Martin Sheen, who, incidentally, was the first pick, but couldn't initially take on the role due to scheduling conflicts.

Two-time Academy Award nominee Samantha Morton was cast as the voice for the AI assistant named Samantha in Her. However, in postproduction, it became apparent that the voice for the AI needed something other than what Morton could bring. "When we started editing, we realized that what the character/movie needed was different from what Samantha and I had created together," said the director of the movie. So the role was given to Scarlett Johansson.

Kel O'Neill was cast in the role of Eli Sunday in There Will Be Blood, together with the household name Daniel Day-Lewis. However, after the filming started, O'Neill wasn't quite the best fit, and even the actor himself realized it. The role was then given to Paul Dano, who was already on set, playing the role of Eli's brother (the script was simply adjusted to include identical twins).

Julianne Moore was let go from her role in Can You Ever Forgive Me a mere 6 days before the filming started. Moore admitted her opinion diverged from the director's: "I think that her idea of where the character was, was different than where my idea of where the character was.” Reportedly, the actress wanted to wear a fat suit to appear more like the real-life person she would portray. Moore was replaced by Melissa McCarthy, who was even nominated for the Best Actress Academy Award.

The Lovely Bones centers its story around a missing girl and her family, and the role of the father was supposed to go to Ryan Gosling, who, in order to better represent the man he was meant to play, put on some weight; Gosling reasoned that he was a stressed father whose daughter was gone, so he thought it was fitting, but director Peter Jackson disagreed, and Gosling was replaced by Mark Wahlberg.

The wonderful talking bear Paddington was originally supposed to be voiced by Colin Firth, but somewhere down the line (after the actor recorded most of the lines), the realization set in that the actor's voice didn't match the animation of the cute bear. “It’s been bittersweet to see this delightful creature take shape and come to the sad realization that he simply doesn’t have my voice.” Firth was replaced by Ben Whishaw.