The Galactic Empire was governed as a dictatorship by Darth Sidious, who was secretly a Sith Lord but publicly known across the galaxy as Emperor Sheev Palpatine.
Dictatorship signifies a form of government where the leader holds unrestricted power and absolute authority, which is the opposite of a democracy.
Back in 22 BBY, Senator Padmé Amidala and Jedi Padawan Anakin Skywalker found themselves temporarily on Naboo to evade a possible assassination attempt targeting Amidala. During this time, they engaged in a discussion concerning the rampant corruption plaguing the Galactic Republic and explored potential solutions. Skywalker suggested that a "wise individual" might be needed to force them to reconcile their differences, leading Amidala to infer that Skywalker was essentially proposing a dictatorship, a notion Skywalker didn't refute, even suggesting it could be effective.
Under the command of Supreme Chancellor Sheev Palpatine, the Galactic Republic, with its parliamentary structure, gradually morphed into a dictatorship. The Chancellor strategically utilized the Clone Wars as justification to modify the constitution and accumulate greater executive powers. As the war concluded, the Republic was officially replaced by a formal dictatorship known as the First Galactic Empire. Other examples of dictatorial rule include Hay-Zu's command over the Patitites, and the governance of the Albee Dewaw—actually a group of DUM-series pit droids—over the Balnab. Both of these regimes were ultimately thwarted by the actions of R2-D2 and C-3PO.