L. Sprague de Camp is one of my favourite early SF writers. I personally think he does a great job linking sci-fi with fantasy concepts in his works. Also, you can feel the words of his texts exuding a massive amount of knowledge of how the world works. I also really enjoy his short stories, maybe even more than his full-length novels to be honest. Can't say that about many authors.
Let's look at some of his amazing cover variants here!