The Archlich mentioned a book called
Guan Yu: The Religious Afterlife of a Failed Hero on tumblr. This is what he said about it:
It’s mostly about the development of Guan Yu as a mythological/religious figure. The historical section is short, since the real Guan Yu (as the author observes) has very little to do with his religious counterpart. It did have some interesting observations, though.
The one I found most striking is Haar’s comment that Guan Yu’s biography is strangely anecdotal. It reads more like a collection of stories about Guan Yu - mostly his personality and conduct - rather than a straightforward account of his career (especially compared to other biographies). Haar suggests that Chen Shou’s biography is derived from an oral history rather than through actual records.
And that makes a lot of sense. Since Shu didn’t establish an official history bureau, Chen Shou’s primary source for records on Shu’s founders was Zhuge Liang’s personal writings. But Zhuge Liang and Guan Yu didn’t actually have much to do with each other. Zhuge Liang obviously wasn’t present for any events of Guan Yu’s life before 208, and the two parted ways in 213.
The history section was all I read of the book, though. I’m not really interested in the subject overall. But Haar at least demonstrated that he knew what he was talking about. If you’re interested in how the cult of Guan Yu developed, it’s probably a good book.
It came out in 2017, I'm not sure how I missed its publication! At some point I will edit into the front page but I thought that it might interest a few people in the meantime!