Palpatine is a human male from Naboo who served as Senator, then Supreme Chancellor, then Emperor, while concurrently operating as the Sith Lord Darth Sidious. He first appeared as a hologram in The Empire Strikes Back (1980), was played on screen by Ian McDiarmid from Return of the Jedi onward, and the given name Sheev was established in James Luceno's novel Tarkin (2014).
The procedural villain
What makes Palpatine frightening in print is that almost nothing he does requires the Force. He wins by controlling the agenda, manufacturing the emergency, and being the only person in the room with a prepared answer. The prequel-era novels — Luceno's especially — are essentially political thrillers in which the reader knows the conspiracy and watches the institution fail to notice it anyway.
Legends: Darth Plagueis
Luceno's Darth Plagueis (Del Rey, 2012) is the definitive text on his rise, and it is Legends. It dramatises the apprenticeship, the Muun Sith Lord who trained him, and the long financial and political groundwork laid decades before Naboo. Nothing in current canon replaces it.
The return
Current canon brought him back in The Rise of Skywalker (2019), and the tie-in fiction has done the work of explaining the mechanism — cloning, the Sith Eternal, Exegol — that the film compresses into a title crawl. Readers' patience for this varies. It is, at minimum, the clearest example of how far the books are now expected to carry a film's load-bearing exposition.
Reading note
Palpatine is best read as an institutional problem rather than a person. He does not defeat the Republic. He persuades the Republic to defeat itself, on the record, by a vote, with applause.
