R. A. Lafferty’s 1968 Past Master is a standalone science fiction novel.
The planet of Astrobe was planned as a utopia, but it is collapsing into lethal civil discord. Determined to preserve their vision, the triumvirate who regard themselves as Astrobe’s governing committee — rich Cosmos Kingmaker, lucky Peter Proctor, and smart Fabian Foreman — do what any concerned person might do in their place: they resort to time-travel to yank a great man out of history to deal with Astrobe’s problems.
And which historic figure has the unique combination of virtues needed to manage the crisis? None other than Thomas More.