Reddit mentions of The Greatest Knight: The Remarkable Life of William Marshal, the Power Behind Five English Thrones

The life of William Marshal, the greatest knight the world has ever known. He served 5 English kings, was regent to the throne, is the only person to best Richard the Lionheart in single combat and at the age of 72 defeated invading French forces and drove them off British soil (and since that day, no invading force has ever landed on British soil). He was George R.R. Martin's inspiration for Barristan Selmy. Everything about his life is unbelievably fascinating. Wiki.

Here are some books I've read about him:
The Greatest Knight by Thomas Asbridge
The Knight who Saved England by Richard Brooks
William Marshal: Court, Career and Chivalry in the Angevin Empire 1147-1219 by David Crouch
William Marshall: Knight-Errant, Baron, and Regent of England by Sidney Painter
William Marshal: The Flower of Chivalry by Georges Duby.

I don't think I'd be able to really stay updated, I never do with that sort of stuff. But, I have a reading list that you should add- that is if you are doing payed books:

For full on historians looking for depth in medieval subjects:

-Asbridge's The Crusades is a far better Crusades history that goes into good depth than any other I've read

-Morris' The Norman Conquest oncemore just a great book for depth and detail

-Jones' The Plantagenets this one I would avoid if you hate sensationalism in history, Dan Jones is a real historian and he writes it as a real historian but he's on the edge of being more entertainer level than educator level

-Moore's 2008 edition of The Formation of a Persecuting Society is definitely the best analysis of medieval heresy I've read

(+ for more details into his actual thought process and the full counter argument to his critics that came out against him later on )

For casual historians looking for analysis and shorter reads:

-Phillip's Holy Warriors is probably an overall better analysis than Asbridge but far less deep, if you like battles go for Asbridge but this is a far shorter read

-Asbridge's The Greatest Knight good book on the Plantagenets through the eyes of the knights

-Golding's Conquest and Colonisation a slightly more boring read, maybe go with the "A short introduction to" book isntead

-Pegg's A Most Holy War for lighter reading on medieval heresy