Dukat wanted power and he wanted to be adored. That's pretty much the summary behind all of his actions to being the "magnanimous tyrant" during the Occupation, to his womanizing, to his constant need of approval from Sisko and Kira. To taking Cardassia into the deal with the devil in season 5. To his final mad foray into Bajoran religion in seasons 6 and 7.
What made Dukat such an interesting character is that he was a complete character. He had a full set of virtues and vices. His patriotism and devotion to duty were almost admirable at times. Heck when he sacrificed his career for Ziyal that was almost noble. During seasons 3-5 you were actively wondering if he was even the "bad guy" anymore.
Far too many villains are just stereotypical. Dukat was nothing but.