The Puppet Masters are an intelligent alien species from Nestor's World, a recently discovered planet in the anti-spinward periphery. They are sessile beings that anchor themselves to the ground and stay in the same spot indefinitely (although they can relocate themselves, under certain circumstances). Lacking mobility and any kind of prehensile organs, the Puppet Masters instead rely on "familiars", specialized semi-independent creatures grown inside the Puppet Masters' gestation pods. The familiars, created through a type of meiosis, share only parts of their parent organism's genetic code and lack intelligence and proper self-awareness. They are directed by the Puppet Masters through a combination of pheromones and highly complex vocalizations and act as their hands and feet, serving their every need. The familiars are capable of venturing far from their parent organism and have a limited capacity for independent operation, although if left without guidance for too long, they can become feral and will usually die off soon thereafter.
The Puppet Master pictured above is surrounded by a trio of "roamers", the most common type of familiar. The roamers are tasked with gathering food and building and operating simple tools, using their prehensile mouth proboscis to manipulate objects. Other types of familiars exist, such as armored "warriors", tasked with defending their master, and "chariots", tasked with transporting the Puppet Master to a new location. Because growing new familiars takes a lot of energy and nutrients, they are usually carefully managed and grown only as needed.
Psychologically, the Puppet Masters are very independent-minded and not very sociable. Each Puppet Master requires a fairly large territory of its own, and thus their population density has always been very low. It has been estimated that there are currently no more than 25,000 Puppet Masters living on Nestor's World. Interaction - including reproduction - between Puppet Master individuals is mainly conducted through familiars. The largest settlements are villages of a dozen or so like-minded Puppet Masters, but even in them, the average distance between individuals is often hundreds of meters.
Nestor's World is a low-light planet orbiting an M-type main-sequence star. It has a unique ammonia-based biosphere with analogues for both terrestrial flora and fauna. Bizarrely, xenoarchaeological studies conducted on the planet and in its star system suggest that the Puppet Masters had an advanced space age civilization comparable to late 21st century Earth... over two million years ago. Then, for reasons unknown, they abandoned their off-world colonies and most of their advanced technology and gradually regressed back to stone age, where they have remained ever since. This regression was not instantaenous, but took at least 10,000 years to complete. So far there has been only limited contact with Human explorers and the Puppet Masters, but apparently the Puppet Masters of today have no knowledge of their ancient civilization, the remnants of which are buried deep in the geological strata of their homeworld.