Fans of "The Clone Wars" will recall that General Grievous' cough is explained during an episode where Mace Windu engages the villain in a duel. As Grievous attempts to flee the battle, Windu uses his Force abilities to crush Grievous' chest plate, with the additional pressure on his chest explaining the cough. But since the aforementioned "Star Wars" series has been removed from official canon, Lucas' original reasoning is now revealed to be slightly different.
Apparently, what Lucas was going for is that, even if technology improves in his galaxy of "Star Wars" characters, it still isn't perfect. So, like Darth Vader (James Earl Jones) himself, though his life is extended by technology after a shuttle crash leaves him mutilated, Grievous also pays a price in terms of this otherwise unexplained malady.
Lost characterization aside, however, you have to admit that the villain is extremely imposing. Upping the ante with four lightsabers being wielded by a single villain is definitely a cool idea, even if General Grievous is ultimately defeated rather unceremoniously around the early to mid-section of "Star Wars: Revenge of the Sith."
