Who are the main characters in Foundation?

Empire, aka the Cleons—Brother Dawn (Cassian Bilton), Brother Day (Lee Pace), and Brother Dusk (Terrence Mann): Differently aged clones of Cleon I, who ruled 400 years prior to season one’s main timeline, though the Galactic Empire has been in place for 12,000 years. They are ostensibly identical, though their personalities have different shades (Dawn is more sympathetic; Day is more cruel; Dusk is more introspective), and as season one progresses we learn that the clones have been compromised by an anti-Empire faction and are not as identical as everyone assumes. The same actors play the different versions of Cleon throughout Foundation, which can be a bit confusing, though the show is careful to give context so you know which Cleon era you’re in.

In season one, the main Cleon storylines involve Day launching an elaborate charade to undermine a potentially powerful religious leader who believes clones don’t have souls, and Dawn, who’s become aware of his anomalies, falling in love with a palace worker who encourages him to run away—only to reveal herself as part of that anti-Empire faction. He’s executed and a new Brother Dawn takes his place.

Demerzel (Laura Birn): Empire’s constant companion, envoy, advisor, and keeper of order; everyone assumes she’s also a clone except the Cleons, who know she’s an android—the very last one after a long-ago war between humans and robots stamped others out of existence. Her loyalty is to Empire, full stop, and though this is an Asimov story, she’s not held to the Three Laws of Robotics. If she needs to kill on behalf of Empire… she will.