Ashley Edward Miller, Zack Stentz, and Don Payne
Makes Sense Out of a Mess
There are three names on the final script for Thor, but IMDB lists six other names accredited with this bad boy…which is Hollywood-ese for "it took them a long time to crank it out."
The Thor saga started at least twenty years before the movie hit screens when director Sam Raimi pitched a Thor movie to 20th Century Fox. They passed—but don't worry: Raimi eventually kicked the superhero movie genre into overdrive by directing the first three Spider-Man movies over at Sony.
"Hey, Maybe We Can Make Money on This Guy!"
After the first X-Men movie turned into a hit in 2000, Hollywood expressed new interest in Thor. Anything from the capes-and-tights department suddenly became gold once the studios realized they could make money with it.
But Thor proved a tough nut to crack, mostly because Thor didn't follow the playbook as far as other superheroes went. The project thrashed around for another eight years until the success of Iron Man made it clear that this superhero needed to be part of that universe.
That's a roundabout way of saying that this story went through a lot of changes in twenty years. The exact placement of who did what is the subject of Hollywood secrecy.
Of the final names on the screenplay, two of them—Ashley Edward Millar and Zack Stentz —were partners know for working mostly on television. That included shows like Fringe and Andromeda, as well as the movie X-Men: First Class (which also hit theaters in 2011).
The last name, Don Payne, also had a background with superheroes, having worked on Fantastic Four: Rise of the Silver Surfer and the bomb My Super Ex-Girlfriend.
Citizen Ken Cracks the Code
The waters get even muddier when Kenneth Branagh finally came on to direct. The team brought in some physicists to "advise" the production…and to make some of the Asgard awesomeness make sense. (Hollywood is awesome.) (Source)
That necessitated further changes to the script: changing Jane from a nurse to a scientist, for instance, and ensuring that Asgard's various doo-dads had at least some grounding in science as discussed in the film.
It was quite a hash, but it all came out right in the end. Considering all of the elements involved and Thor's one-of-a-kind status among all things superhero, we shouldn't have been surprised.