gffa:
All the main villains of the prequels movies were reflections of the villain that Anakin Skywalker was to become.
Darth Maul was the Sith apprentice, one that was never valued by the Sith and always had to prove his place with them, the one who was so steeped in the dark side that he couldn’t see any of the paths out of there back to the light. He is replaced by Sidious as soon as a new, younger apprentice comes along. He is the one who hates himself as much as he hates those around him, suffering in the dark all alone.
Count Dooku was the fallen Jedi, the one who believed he had power greater than any other Jedi, just as Anakin believed that he would find a way to be the most powerful Jedi ever. He is a reflection of Vader staring up at his Master directly in the face, unable to truly comprehend that his end has come this way, he is the choice that Anakin makes to destroy him, while Luke chooses mercy when in the same situation.
Grievous is the one who uses his artificial limbs and body to push away his humanity (/alien equivalent thereof), that both Grievous and Vader use mechanical parts, but so too does Luke Skywalker, and that’s not the issue, the issue is that they use this to separate themselves from compassion for others, one who never cares for the people or droids that work under him.
Each of these villains was designed to echo and rhyme with an aspect of Darth Vader and the prequels do not get enough credit for it!