The illustrator Robert K. Abbett was born in Hammond, Indiana and educated at Purdue and Missouri Universities. From the 50s through the 70s, Abbett was prolific commercial illustrator, painting covers for Ballantine Books, Pyramid Books, and Ace Books. Though his best known work are the covers that he did for the John Carter of Mars series, Abbett worked in all genres.
Here’s a small sampling of his work:
By Paul Rader
by Robert Bonfils
by Harry Barton
Artist Unknown
Artist Unknown
by Rudolph Belarski
Artist Unknown
All the covers below were done by Al Rossi, who painted several paperback covers in the 50s and 60s. I haven’t been able to find much information online about Al Rossi. Maybe someone who worked with or knew Al Rossi will come across this post and leave a comment. It’s happened in the past. Until then, his work will have to speak for itself:
Unknown Artist
Through the Shattered Lens 