Written by The reason for General Grievous' cough has changed in the canon story, and is still somewhat a subject of debate
When General Grievous was first revealed in ‘Revenge of the Sith‘, it was hard not to see the gruesome villain as deadly and menacing. But just as the goosebumps start to form, the metallic skeletal-like villain reveals he’s got a major flaw: a cough that breaks the threat of his presence and replaces it with obvious vulnerability. Make no mistake- fans know from watching ‘The Clone Wars’ series that Grievous is extremely deadly, killing Jedi without a second thought and collecting their lightsabers as if he were on a causal trophy hunt in the safari. But just as Grievous is deadly, he’s a contradiction – plainly showing weakness wherever he goes.
While the origin of his cough was once debated and then believed to be decided, the canonized reasoning has actually debunked the original theory in favor of a more scientific explanation. The original explanation came from the animated miniseries, Star Wars: The Clone Wars, in which General Grievous leads an attack on Coruscant, successfully capturing Chancellor Palpatine. Just after capturing the Republic’s highest leader though, Grievous was about to take off in a ship to leave when Jedi Master Mace Windu landed on the scene.
Realizing that he was too far away to duel the cybernetic general and try to retrieve the chancellor, Windu settled with using the Force to crush Grievous’ rib cage and abdominal compartments, leaving the General in a coughing fit just as his ship escaped. Since then, it had generally been accepted that this was the reason for Grievous’ cough as seen in ‘Revenge of the Sith‘.
Star Wars: The Clone Wars ministeries: Mace Windu crushes General Grievous' ribcage:
But in 2014, along with most other Star Wars material that wasn’t directly in the first six films, this miniseries became non-canon, making it Legends material that could no longer seriously be used to explain the origins of General Grievous’ cough. With the miniseries no longer a valid source, fans had to look elsewhere to determine the reason for the Separatist cyborg leader’s cough. Though, to date, Disney hasn’t released any official statements regarding Grievous’ asthmatic malady, an old 2007 documentary did shed some light on the subject providing a largely foundational explanation that has widely been accepted as an official explanation.
The documentary, Star Wars: The Legacy Revealed, which principally explores the impact the original 1977 Star Wars film has had upon society and filmmaking, also explains that George Lucas added Grievous’ cough into the plot for a reason entirely unrelated to Mace Windu. According to Lucas, the cough wasn’t the result of a lung injury or illness – it was in fact a result of the imperfect cybernetic technology that was used to create Grievous. Before becoming cybernetic, the Kaleesh general, whose name was originally Qymaen Jai Sheelal, eventually chose to undergo massive surgery, having his organs encased in a powerful cybernetic body with enhanced reflexes and deadly abilities. Despite his menacing transformation, the cybernetic technology was unable to fully supply him with a properly-functioning respiratory system, thus requiring him to periodically cough, presumably to clear secretions at the site of oxygen exchange.
In reality, the original decision to give General Grievous a cough was more of an afterthought than a calculated decision. In the DVD commentary track for ‘Revenge of the Sith’, it’s revealed that Lucas came to work and had a bit of a coughing fit, inspiring him to give Grievous a more unique character by adding the cough.
Regardless of the amount of forethought that really went into deciding to add this vulnerability, Lucas’ official explanation actually provides a deep insight into the technologic development and advancement in the Star Wars galaxy. We see that, despite the technology’s impressive abilities, still it had not yet been mastered and had critical imperfections. Star Wars theorists believe that Palpatine actually had manipulated events to encourage the talented Kaleesh general to wear the suit. Palpatine was then able to learn from this mistake when it became necessary to place Darth Vader in a similar life-sustaining suit. By learning from Grievous’ imperfections, Vader could be born as a menacing Sith Lord without any respiratory issues. Further cybernetic technology would be fully mastered by an eventual opponent that the Emperor would actually use to test Vader – a cybernetic mad scientist named Cylo.
Another instance where the extended verse is better than canon.