This cover illustration may not be striking enough to pull your attention from across the room. There's nothing particularly wrong with it, it just isn't an overwhelmingly dynamic composition or subject matter.
There's a guy patching a hole in what appears to be a giant space balloon holding atmosphere for people inside. Not horrible, but not inspiring. As usual when this is the case, I start to look around at what was happening in the world.
As it turns out, 1964 brings us some amazing space stories, such as the "Afronauts".
The US and the Soviet Union were deep in competition at this point, pushing further and further outward, with sights set on the moon. A Zambian school teacher named Edward Makuka Nikoloso, inspired by Zambia's recent independence, created the space program that he dubbed the "Afronauts" and claimed that they would be the first to the moon, beating the two super powers.
To put it simply, they didn't have the technology, training, or funding to do anything of the sort. They lacked support from their local government and ultimately dropped their plans after the pilot of their ship, 17 year old Matha Mwambwa, became pregnant.
Publication: Worlds of IF Science Fiction
Issue: August 1964, volume: 14 No. 4
Cover art: Fetterly from The Slaves of Gree
Now this would have been a hell of a cover! not only is it much more intriguing, it is for the same story and by the same artist.
The quad-globed space domicile pictured in the top immediately brings to mind a childhood toy that I enjoyed, Capsella.
Wow, Morrow certainly nailed the bad guy stereotype of the era. Here's the description of this character. I suspect that Morrow skimmed this, saw the beard, horns, and mustache and just went with something familiar.
Gree was certainly humanoid, if one could elevate the word. He was tall; taller than Jen or Fazzoool or the Overseer by perhaps a foot. His shoulders were broad, his build supple and young. But the gray strands in his curly black hair and beard showed his maturity. he wore a suit of dark material which almost certainly had precious metals woven into it. At his throat a jabot of the purest white cloth set off the short-cropped beard and his olive skin. the face was just sufficiently marked with care. The eyebrows arched up and tilted at the outer ends almost mischieviously. the eyes were very long and narrow, with full lashes and long folds of skin at the inner corners. The irises were very light gray and had black vertical slits for pupils that looked into one's soul for the slightest shadow of unworthiness. Jen Shuddered and was glad he bore no flaws.
The nose, delicate at the bridge, swelled to a very broad base a trifle uplifted so it showed large nostrils. There was a curl of mustache above the wide, full-lipped mouth. The mouth seemed both stern and faintly smiling at the same time. The skin drew in tautly under sharp cheekbones, to a gaunt jaw that was square and outthrust under the beard. On the head, set hair like two tree-trunks, were two horns, straight, an inch thick and five inches long, with blunt knobby ends. They were intricately carved and inset with gems, and they held Jen's eyes in fascination.
I haven't read this story. At a glance, it seems like a fun bit of anachronism, mixing aliens and midievel imagery. I have to say that a jolly roger on a flying saucer makes me smile. This might be worthy of being made into a sticker.