Pierson's Puppeteers have two forelegs and a single hindleg ending in hoofed feet and two snake-like heads instead of a humanoid upper body. The heads are very small, containing a forked tongue, extensive rubbery lips, rimmed with finger-like knobs, and a single eye per head. The Puppeteer brain is housed not in the heads, but in the "thoracic" cavity well protected beneath the mane-covered hump from which the heads emerge.
They use the "mouths" to manipulate objects, as a humanoid uses hands. The Puppeteer's native language sounds like highly complex orchestral music, but they seem to be able to reproduce human language without difficulty or device, as well as the Heroes' Tongue (Kzinti), suggesting their vocal arrangement may resemble a pair of avian-like syrinx rather than vocal cords. The sobriquet "Pierson's" comes from the name of the human who made first contact in the early 26th century in the Known Space timeline.
Biologically, Puppeteers are highly intelligent herbivores; a herd animal, Puppeteers prefer the company (and smell) of their own kind. Their cycle of reproduction is similar to that of Earth's digger wasps: the Puppeteers consider themselves to have three genders (two male, one female): the two "male" genders are the equivalent of human female and male (one has an ovipositor, the other produces sperm) and the "female" is a (non-sentient) parasitized host into which the ovum and spermatozoon are deposited.
Puppeteers are very long-lived. The exact length of a Puppeteer's lifespan is unknown, but it is at least several centuries. This, together with a total lack of contraceptives (except major surgery) for their species, is responsible for extreme crowding: the Puppeteer homeworld has a population of over a trillion, and four farming worlds are dedicated entirely to supplying the population with food.
Technologically, the Puppeteers are very advanced, centuries or millennia ahead of most other species (including humans). For example, humans in Niven's universe invented a method of cheap teleportation in the twenty-fifth century called a transfer booth, which requires an enclosed space at either end of the transmission. Puppeteers use a much more elegant and sophisticated booth-less "open" version in the form of stepping disks, which require no enclosure.
Socially, two notable traits of Puppeteers are their racial/cultural penchant for cowardice and their tendency to congregate in herds. The cowardice is thought in Puppeteer society to originate with the Puppeteer instinct for turning one's back on danger. However, the trait is thought by many to actually originate from their herd instinct, as the instinct to turn one's back is linked to an instinct to kick the hind hoof at an attacker. In Ringworld, when Nessus and the expeditionaries are threatened, the Puppeteer defends himself quite effectively.
Another behavioral trait is the coma state, broadly a cognate of the human fetal position–in the same way that ostriches are said to bury their heads in the sand, Puppeteers fold up into a ball, tucking their three legs and two heads underneath the padded cranial bulge. This is, in part, an explosion reflex, learned during childhood. Their cowardice is also reflected in their architecture and object design, as all the Puppeteer-designed rooms and vessels have no sharp edges, everything curves into everything else, giving a "half-melted" look and meaning that objects are less likely to damage someone inadvertently, through their own carelessness.
For centuries, the location of the Puppeteer homeworld was a great mystery. No entity in Known Space outside the Puppeteer race was aware of the location, despite extensive surveys, with the probable exception of Jinx-born pirate Captain Kidd. In the short story "A Relic of the Empire", he discovered the Puppeteer home system by accident, and returned in the ship Puppet Master to rob inbound Puppeteer vessels, rather than pursuing a formal blackmail arrangement. Kidd claimed the Puppeteers' home planet orbited a "red giant, undersized", in the vicinity of coordinates 23.6, 70.1, 6.0 (using an unnamed coordinate system). Before dying, he passed this location along to Richard Shultz-Mann, of the planet Wunderland.
Puppeteers were willing to pay large sums of hush money in order to suppress even trivial details about their homeworld. In 2641 AD, it was discovered that the Puppeteers' homeworld? had no moon, information deduced as a result of the solving of the mystery of the deaths of a crew of a ship investigating a neutron star. The ship, based on a General Products hull, was impervious to tidal forces but the crew were not. Because the Puppeteers seemingly have no experience of tides, they were unable to anticipate the deadly tidal forces. (As told in Niven's short story, "Neutron Star")
The Puppeteers had to make some drastic alterations to their home system, during their history, as waste heat due to overindustrialisation was rapidly making their planet uninhabitable. They moved their planet further from their sun, to lessen the effects of global warming, but overindustrialisation forced them to move four of the other planets in their system closer to their world and terraform them into "farming worlds", arranging the five planets into a Klemperer rosette.
Eventually, their sun converted from a yellow dwarf to a red giant, so the Puppeteers moved the "Fleet of Worlds", the five planets, to their system's Oort cloud. This is one of the reasons the Puppeteers were so successful at keeping the location of their homeworld a secret—explorers would be looking for a yellow dwarf (as one could surmise that Puppeteers had evolved around a yellow dwarf from their biology and that they were comfortable on Earth-like planets without pressure suits) when their planet(s) were actually near a red giant.
Politically, the Puppeteers have a form of democracy with two major parties: the Conservatives and the Experimentalists. The Conservatives have held power for a majority of Puppeteer history; Experimentalist regimes only take power when a crisis threatens the safety of the Puppeteer race, and action is considered less dangerous than inaction.
The general foreign policy of Puppeteers consists of attempts to control the universe around them to ensure their own safety. As Puppeteers try to expose themselves to as little risk as possible, they try to use other beings as agents, utilizing a combination of bribes and blackmail to encourage cooperation. Blackmail is not immoral to a Puppeteer and Puppeteers have an established code of conduct surrounding the practice, making it perfectly safe for both the blackmailer and the victim, including that the blackmailer must turn over all their evidence against the victim and submit to a partial memory wipe, so they cannot betray the blackmail deal. The Puppeteers also use more personal manipulation; for instance, Puppeteers who have dealt with human males have utilized a voice that sounds like that of a seductive human female, and the Puppeteer Nessus utilized an implanted tasp, a device which could stimulate the pleasure center of the brain, thus allowing him to subliminally condition those he dealt with.
The Puppeteers' renown for honesty in trading allowed the species to accumulate an expansive mercantile empire called General Products; since the human Bronze Age, the Puppeteers have ruled this empire including every race in the 60-LY sphere of Known Space. One of the most important items sold by General Products is the General Products Hull for spaceships. As one might expect from a Puppeteer, such a hull is completely impervious to everything except antimatter (which is not highly advertised but covered by a company warranty; the hull is transparent to visible light which can be alleviated by polarization or complete opacity; tidal forces and extreme gees will not affect the hull but can kill the occupants, unless nullified by variable cabin gravity.) The hulls are advertised as being capable of flying through the upper atmosphere of a star unscathed, although the contents will be cooked; as a protection against this particular contingency, the Puppeteers also provide a stasis field.
Sources and references: Neutron Star, A Relic of the Empire, At the Core, Flatlander, The Soft Weapon, The Color of Sunfire, Ringworld, The Ringworld Engineers, Fleet of Worlds, Barlowe's Guide to Extraterrestrials,