A bunch of famous names. Some of the later guys are North American.
Early: Classics by T.E. Pryce-Tannatt, John James Hardy, George Kelson give late 19th/early 20th century history of salmon flies and technique (Tannatt's is a great book). These should be easily located as free texts on the internet.
Mid: Hugh Falkus, Richard Waddington (his Philosophy and Practice... is still maybe the best), and John Veniard take you through mid-century. Lee Wulff's Bush Pilot Angler about mid-century salmon fishing in Newfoundland is a fantastic book.
"Modern": From the 70s-80s, Keith Fulsher (Charles Krom) has a nice book on the transition to hair wing flies, and Poul Jorgensen and Joseph Bates have famous titles too.
Contemporary: These guys have books too, but they're are so omnipresent on the web in various articles and videos that I haven't read them in print. Look for Alastair Gowan, Mikel Frodin, Topher Browne, and Hans Van Klinken among others.