Leo Frankowski's Conrad Stargard Series

Conrad Stargard
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Conrad Stargard is the protagonist and title character in a series of time travel novels written by the Polish American writer Leo Frankowski. In them, a Polish engineer named Conrad Schwartz is sent back in time to the 13th century where he has to establish himself and cope with various crises including the eventual Mongol invasion of Poland in 1240.
The character of Conrad has at times been described as a Mary Sue, and some aspects of the novels can be looked at as authorial wish-fulfillment. In response to this criticism in an early draft of the first book, Frankowski modified the character to have the opposite traits as himself, such as Conrad's socialism and devout Catholicism.[1]
The series originally consisted of four books, with a fifth released shortly after to wrap up loose ends. They are:
The Cross Time Engineer
The High Tech Knight
The Radiant Warrior
The Flying Warlord
Lord Conrad's Lady
all originally published by Del Rey Books, and recently being released by Baen Books.
A later sequel, Conrad's Quest For Rubber is set in the same world/timeline as the original series but does not feature Conrad as its main protagonist.
Another book of Frankowski's, Conrad's Time Machine is set in the same universe as the original series and is only loosely related, having to do with the invention of the time machine with which Conrad ends up in the 13th century.
In late 2005, Frankowski self-published Lord Conrad's Crusade with Conrad Stargard again as the protagonist.
The Conrad Stargard books clearly belong to the subgenre started by Mark Twain's classic A Connecticut Yankee in King Arthur's Court, in which a modern person goes back in time and anachronistically introduces various modern technical innovations and social institutions centuries sooner than happened in our history.
The Stargard books differ significantly from Twain's concept in having a diametrically opposite role for the Catholic Church. The staunchly Freethinking Twain assigned to the Medieval Church the role of strongly opposing his protagonist's innovations and doing all in its power to undo them; on the contrary Frankowski - of a Polish Catholic background - provided his own time traveler from the very moment of arrival in the past with a friendly and sympathetic clergyman, who steadily rises in the Church hierarchy and ensures that the Church adopt a benevolently neutral attitude to Conrad's various enterprises, considerably helping their success.

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