I know ‘**Pietr le Letton**’. This detective novel was published in 1931 by Belgian novelist Georges Simemon. In this novel, Latvian appear as the boss of a notorious Baltic gang.
[The Strange Case of Peter the Lett – Wikipedia](https://en.wikipedia.org/wiki/The_Strange_Case_of_Peter_the_Lett)
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Project [Imaginary Latvians](https://imaginarylatvians.com/) might interest you – they list all Latvian characters that appear in books and movies. And by the way, this Peter the Lett seems to be based on a real Latvian guy, [Peter the Painter](https://eng.lsm.lv/article/features/features/latvias-got-personality-international-man-of-mystery-peter-the-painter.a427865/), who managed to make quite a reputation.
In Stephen King’s novel Stand they mention Latvia