He’s essentially a space-Nazi.
The ultimate in Star Trek villainy, Gul Dukat lead the Cardassian forces on Deep Space 9 before the occupation of Bajor ended. Like all good villains, Dukat always claimed they were there to save the Bajoran people, and that had they accepted the help of the Cardassian’s that Bajor would’ve prospered like never before.
All lies, obviously, as the Cardassians constantly tortured, brutalized, maimed, and did worse to the people of Bajor.
When Benjamin Sisko came in as Dukat’s foil, the two men bounced off one another like a superball in a tiny room. Their leadership styles showed so much similarity but were so different. Dukat spoke to many people as a friend, until he was displeased by something, then the monster would come out. The inverse was true for Sisko, who often took a stern and gruff exterior to show his authority but was quick to remind someone of his own humanity when the need arose.
The parallel between Dukat and Sisko really amplified the sinister nature of Dukat, allowing the audiences to grasp and understand the depth and vile nature of that man by holding up a mirror to a more contemporary personality in Sisko, who while never perfect, always did what he thought was right. The inverse for Dukat was true, as he always tried to do what would be the most beneficial thing for him.
This coupling was necessary for the show to stand out on its own and away from the other shows. It made the series a hit, even 25 years later. Dukat’s brilliance as a villain can only be truly enjoyed from start to finish. So fire up those DS9 DVD’s or streams and get to watching.