John D. MacDonald is the only writer I ever wrote a fan letter to. This was back in the 1970s, when I was in Junior High, and I never got an answer. I wish I had a copy of that letter now. I can't remember what it said; I just remember sending it. At the time I was enamored of JDM's Travis McGee series. McGee was a Knight errant with slightly tarnished armor, and I loved his appearances in such books as The Turquoise Lament, The Deep Blue Goodbye, and The Long Lavender Look. JDM wrote 21 books in the McGee series, and all but the last to be published, The Lonely Silver Rain, were truly excellent. He also wrote many other books as well, over 70, and the vast majority of them were a combination of noir, mystery and thriller. My favorite, non-McGee book, is called Murder in the Wind, which involves a group of people trapped in a house during a hurricane and which I think is a lesson in how to write a thriller.
MacDonald died in 1986, the same year I finished graduate school, and I've read almost everything he's ever written. I would have read it all, but I've actually been doling the last few books out to myself over time. I hate to think of when they are all gone. Right now I'm reading Judge Me Not, about an anti-corruption crusader who runs head on into some nasty corrupters. This was published in 1951, from Gold Medal Books, and is one of his earlier efforts. It's not the best thing JDM did, but it still has the magic and I'm enjoying it quite a lot. If you haven't read any JDM, try his McGee books first. If you're into SF more, he also wrote a few SF novels, Wine of the Dreamers, Ballroom of the Skies, and The Girl, The Gold Watch, and Everything. They made a TV movie from the last one, and since that time a couple of movies have borrowed the basic idea. It's very good, about a man who has a watch that can stop time, but my favorite among his SF pieces is Wine of the Dreamers.