These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Designated Villain: Salvador Hassan O'Leary is the intended villain, despite not being anywhere near as bad as Dr. Benway and only being slightly worse than A.J.
Ensemble Darkhorse: Dr. Benway, by far the most memorable character in the book, goes on to get small roles in several other Burroughs novels, like The Soft Machine, Cities of the Red Night, and The Western Lands, with brief mentions in several others. In The Film of the Book, he's a One-Scene Wonder (well, two scenes) and is played by Roy Scheider. Scheider is appropriately scene-stealing, even when (during one of the two scenes) as Benway he's pretending to be an ordinary doctor running a clinic.