1931: alien cyborgs
"The Jameson Satellite", a novelette by Neil R. Jones, the beginning of his Professor Jameson series; first published in Amazing Stories, July 1931; available at Project Gutenberg and the Internet Archive. (The image above shows the February 1932 Amazing Stories with cover by Leo Morey illustrating the second story in the series.)
Rating not even a cover mention, the first installment of Jones' most popular creation, "The Jameson Satellite", appeared in the July 1931 issue of Amazing Stories. The hero was Professor Jameson, the last Earthman, who became immortal through the science of the Zoromes. Jameson was obsessed with the idea of perfectly preserving his body after death and succeeded by having it launched into space in a small capsule. Jameson's body survived for 40,000,000 years, where it was found orbiting a dead planet Earth by a passing Zorome exploration ship. The Zoromes, or machine men as they sometimes called themselves, were cyborgs. They came from a race of biological beings who had achieved immortality by transferring their brains to machine bodies. They occasionally assisted members of other races with this transition (e.g. the Tri-Peds and the Mumes), allowing others to become Zoromes and join them on their expeditions, which sometimes lasted hundreds of years. So, much like the Borg of the Star Trek series, a Zorome crew could be made up of assimilated members of many different biological species. The Zoromes discovered that Jameson's body had been so well preserved that they were able to repair his brain, incorporate it into a Zorome machine body and restart it. The professor joined their crew and, over the course of the series, participated in many adventures, even visiting Zor, the Zorome homeworld, where he met biological Zoromes. The professor eventually rose to command his own crew of machine men on a new Zorome exploration ship. "The Jameson Satellite" proved so popular with readers that later installments in Amazing Stories got not only cover mentions but the cover artwork. The series eventually became some of the most popular and well-known of the 1930s pulps.
Description of the Zoromes:
Within the interior of the space traveler, queer creatures of metal labored at the controls of the space flyer which juggernauted on its way towards the far-off solar luminary. Rapidly it crossed the orbits of Neptune and Uranus and headed sunward. The bodies of these queer creatures were square blocks of a metal closely resembling steel, while for appendages, the metal cube was upheld by four jointed legs capable of movement. A set of six tentacles, all metal, like the rest of the body, curved outward from the upper half of the cubic body. Surmounting it was a queer-shaped head rising to a peak in the center and equipped with a circle of eyes all the way around the head. The creatures, with their mechanical eyes equipped with metal shutters, could see in all directions. A single eye pointed directly upward, being situated in the space of the peaked head, resting in a slight depression of the cranium.
These were the Zoromes of the planet Zor which rotated on its way around a star millions of light years distant from our solar system. The Zoromes, several hundred thousand years before, had reached a stage in science, where they searched for immortality and eternal relief from bodily ills and various deficiencies of flesh and blood anatomy. They had sought freedom from death, and had found it, but at the same time they had destroyed the propensities for birth. And for several hundred thousand years there had been no births and few deaths in the history of the Zoromes.
This strange race of people had built their own mechanical bodies, and by operation upon one another had removed their brains to the metal heads from which they directed the functions and movements of their inorganic anatomies. There had been no deaths due to worn-out bodies. When one part of the mechanical men wore out, it was replaced by a new part, and so the Zoromes continued living their immortal lives which saw few casualties. It was true that, since the innovation of the machines, there had been a few accidents which had seen the destruction of the metal heads with their brains. These were irreparable. Such cases had been few, however, and the population of Zor had decreased but little. The machine men of Zor had no use for atmosphere, and had it not been for the terrible coldness of space, could have just as well existed in the ether void as upon some planet. Their metal bodies, especially their metal-encased brains, did require a certain amount of heat even though they were able to exist comfortably in temperatures which would instantly have frozen to death a flesh-and-blood creature.
Their alphanumeric designations:
These machine men had no names and were indexed according to letters and numbers. They conversed by means of thought impulses, and were neither capable of making a sound vocally nor of hearing one uttered.
"Where shall we go?" queried one of the men at the controls questioning another who stood by his side examining a chart on the wall.
"They all appear to be dead worlds, 4R-3579," replied the one addressed, "but the second planet from the sun appears to have an atmosphere which might sustain a few living creatures, and the third planet may also prove interesting for it has a satellite. We shall examine the inner planets first of all, and explore the outer ones later if we decide it is worth the time."
"Too much trouble for nothing," ventured 9G-721. "This system of planets offers us little but what we have seen many times before in our travels. The sun is so cooled that it cannot sustain the more common life on its planets, the type of life forms we usually find in our travels. We should have visited a planetary system with a brighter sun."
"You speak of common life," remarked 25X-987. "What of the uncommon life? Have we not found life existent on cold, dead planets with no sunlight and atmosphere at all?"
"Yes, we have," admitted 9G-721, "but such occasions are exceedintly rare."
"The possibility exists, however, even in this case," reminded 4R-3579, "and what if we do spend a bit of unprofitable time in this one planetary system—haven't we all an endless lifetime before us? Eternity is ours."