Believe it or not, when a film's script is written, it sometimes doesn't turn out at all like originally planned by the screenwriter.
Sometimes the studio execs come in and make widespread changes, and sometimes lazy producers fiddle with the idea to turn it into a ready-made sequel for an existing film.
7. 10 Cloverfield Lane
In early 2016, 10 Cloverfield Lane seemingly came out of nowhere and was released almost as soon as it was announced.
Unlike all the other entries on this list, the 'spiritual successor' to ground-breaking monster movie Cloverfield had actually been made and was awaiting a release when it was turned into a sequel.
The script was originally called The Cellar as an "ultra low budget" spec script when it was picked up by Paramount Pictures, who then brought in Whiplash writer/director Damien Chazelle to work on it under the codename Valencia to keep the plot details a secret.
As production went along, the filmmakers noticed similarities to Cloverfield, and producer J.J. Abrams decided to turn it into "a blood relative" or "spiritual successor" of Cloverfield.
Cast members Mary Elizabeth Winstead and John Gallagher admitted that even they were kept in the dark about the decision until they were told it was going to be called 10 Cloverfield Lane a couple of days before its release.
6. Speed 2: Cruise Control
When Speed was a hit in 1994, director and producer Jan de Bont was tasked with coming up with a second take on 'the bus that couldn't slow down' idea that proved so successful.
Graham Yost, the writer of the original Speed, provided a couple of ideas, including a Vietnam War-era vessel loaded with weapons that would explode if its ammunition came in contact with water, or a plane that has to fly through the Andes mountains, but cannot ascend above 10,000 feet.
With hundreds of ideas submitted for the sequel, de Bont turned down all of them in favour of one based on a recurring nightmare he had about a cruise ship crashing into an island.
Fortunately for de Bont, a script, originally titled Troubleshoot had been picked up as an idea for Die Hard with A Vengeance which saw John McClane fighting terrorists on a Caribbean cruise line.
That idea was dropped for being too similar to Under Siege, which meant that da Bont could repurpose the script for a massively disappointing Keanu-less Speed sequel.
Speaking of Under Siege...
5. Under Siege 2: Dark Territory
It's funny that the Die Hard producers thought the eventual Speed 2 script with John McClane fighting terrorists on a boat was too similar to the original Under Siege, which was actually a rip-off of the first Die Hard - proving the cyclical nature of Hollywood.
After Under Siege, wanting to keep his career as 'samey' as possible Seagal signed on to star in an unrelated filmed named Dark Territory, about terrorists hijacking a train for nefarious reasons.
Hearing this, and looking to take advantage of Under Siege’s popularity, the producers brought in L.A. Confidential writer Brian Helgeland to adjust the Dark Territory script to be an Under Siege sequel set aboard a train rather than a battleship.
They kept the original script's title, resulting in the middle-of-the-road Under Siege 2: Dark Territory.
4. Saw II
After Saw was a massive hit with horror fans, the producers wanted a sequel but the creators, James Wan and Leigh Whannell, were working on the ventriloquist dummy horror Dead Silence.
Enter Darren Lynn Bousman - who had written a script called The Desperate, which was turned down by studios for being too violent and too 'Saw-ish' to turn into a film.
Producers Twisted Pictures discovered Bousman's script, and thought (with a bit of rewriting) it would fit perfectly into the Saw franchise.
With Wan and Whannell's assistance, Bousman developed the script into a fully-fledged Saw sequel, for which he was given directing duties (as well as the next two Saw instalments).
The characters, traps and deaths were kept in, but according to Bousman: "You could read the script for "The Desperate" and watch Saw Ⅱ, and you would not be able to draw a comparison".
3. Die Hard with a Vengeance
The first two Die Hard movies were based on adaptations or other scripts and so, wanting to do it properly for the third film, the studio set about writing scripts for Die Hard with a Vengeance.
Bruce Willis rejected each and every one because they felt like low-rent versions of the first film, (like Under Siege).
Meanwhile, Warner Bros. were developing a fourth Lethal Weapon movie and bought a spec script called Simon Says, which planned for Brandon Lee to play the lead, and set about rewriting it for another Riggs and Murtaugh adventure.
Warner later changed their minds and threw out their rewritten version of Simon Says, and in stepped 20th Century Fox, who once again rewrote it into the third Die Hard movie.
Remnants of Warner's plans for Lethal Weapon 4 remain in Die Hard with a Vengeance, most notably in the 'buddy cop' relationship between John McClane and Zeus Carver, which was obviously planned for Riggs and Murtaugh.
2. Ocean's Twelve
The Adjustment Bureau writer/director George Nolfi was working on a spec screenplay that he had named Honor Among Thieves about America's greatest thief coming up against Europe's greatest thief and the pair trying to outdo each other in the thievery stakes.
Ocean's Eleven producer Jerry Weintraub found the script and noted its similar tone to Ocean's Eleven, and wanting to push out a sequel after the success of the star-studded heist movie, saw the potential for Nolfi's script to be reworked.
Nolfi set about rewriting the script, with input from Weintraub and director Steven Soderberg, turning it into Ocean's Twelve.
Unfortunately, the sequel didn't see the same success as the first film, including a climactic twist that didn't fit in with the film's story up to that point; but despite that, another sequel, Ocean's Thirteen came along.
1. Evan Almighty
Back in 2004, Josh Stolberg, writer of Piranha 3D, saw his script become the subject of a seven-studio bidding war eventually being snapped up by Sony in a deal with $2.5m - the record for a spec script with an unknown writer.
The script was titled The Passion of the Ark, a comedy about a modern-day Noah.
Sony hired The Nutty Professor and Patch Adams screenwriter Steve Oedekerk to edit the script and formed it into a Jim Carrey-less sequel to Bruce Almighty, which saw Steve Carrell's character Evan Baxter build an ark on the advice of God (Morgan Freeman).
With a $140 million budget, it was the most expensive comedy film ever made, and while it didn't go down well with fans and critics, it earned a respectable $173 million worldwide.