Darth Sidious

Darth Sidious, also known as The Emperor, is the main villain of the Star Wars films. Sidious manipulates the Senate to proclaim himself Emperor, and manipulates Anakin Skywalker into becoming his apprentice. He is an unabashedly evil man and takes great delight in the suffering of others, especially when they suffer yet continue to serve him. He is controlling and his ability to make reasonably accurate predictions of the future causes him to know all of the cards before they're even in his hand.

He is ultimately defeated not by Luke Skywalker, but by his own subordinate, Darth Vader. He did not foresee Vader wising up and casting him into a reactor shaft, hinting at an egotistical nature that does not see what he feels he controls utterly as anything but tools.

Later in the Expanded Universe, there are debacles with clones of his. The man even had contingency plans for death, it seems.

Darth Sidious in Fanfic
Most Star Wars fanfiction barely mentions him, except in passing or in his original role. He is not a common (or even vaguely present) Lust Object, and his evil nature is completely beyond redemption. Sometimes goodfic will include him to a degree, but most mediocre fic doesn't concern him or doesn't even bring him into the conflict.

Darth Sidious in Badfic
Darth Sidious is mostly seen as a 'dirty old man' because of his ugly appearance, and as an obstacle to Sues going after either Darth Maul or Anakin Skywalker. He is sometimes bashed by badficcers, making him far too easy to defeat or causing him to be much more stupid than he really is. In reality, he is an insanely powerful Sith Lord and was capable of defeating Yoda in single combat. He was able to manipulate the Republic into becoming an Empire. Portraying him as a minor threat or making him stupid are probable charges.