Not all Sith are created equally. In a post on the Star Wars: The Old Republic website, BioWare writer Rebecca Harwick discusses the reasons behind the creation of the Sith Inquisitor, the Emperor Palpatine to the Sith Warrior's Darth Vader.
As Rebecca points out, that comparison is apt, but it does sell the class short. "It's not the destination, or the road we take to get there, but the guide. The Sith Inquisitor is Raistlin. The Sith Inquisitor is Lucifer. The Sith Inquisitor is Julius Caesar. The Sith Inquisitor is what you make him."
But why did BioWare make him?
When we set out to build our game, we knew we needed more than one Sith class. The original trilogy only has two Sith in it, but they couldn't be more different: the heavily armored brutal physicality of Darth Vader compared to the frail but immensely powerful Emperor Palpatine. When we extend our inspiration to Episodes I-III and The Clone Wars cartoons, Count Dooku, Darth Maul, and Asajj Ventress further expand our concept of what a Sith can be. Is a Sith a lithe quick fighter who uses the Force to enhance his/her physical combat prowess, a calculating deceiver adept at Lightsaber duels, or a master manipulator and amasser of dark side secrets? Does a Sith use one lightsaber, two Lightsabers, or a dual-bladed Lightsaber? Having multiple Sith classes allows us to embrace all of those Sith inspirations, instead of having one Sith class that was the jack-of-all-trades and the master of none.
It's also about exploring the Sith order from two different perspectives. While the Sith Warrior is groomed from birth to become a dark master of the Force, pampered and spoiled, the Inquisitor starts life as a slave, taken by the Empire because of his Force-sensitivity, given the choice of becoming an Inquisitor or dying.
The Inquisitor quickly learns that the opportunity the Sith promises if he passes his trials comes with its own set of rules and masters. The so-called freedom of the Sith is reined in by deep traditions and a society where the powerful do their utmost to keep their inferiors under control.
Suddenly the Raistlin comment becomes much more appropriate.
You can read the entire entry at the link below. It's an interesting look into the story-driven process behind the development of Star Wars: The Old Republic, direct from someone responsible for crafting that story.
Composing the Sith Inquisitor [Star Wars: The Old Republic]