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The Trill (or Trills) referred to two species from the planet Trill; one was humanoid and distinguished by a pattern of spots from the top of their head to their toes, and the other was a symbiotic slug-like organism called a symbiont. The symbionts would often "join" with a humanoid host so they could experience the universe at large. The symbionts distinguished humanoid Trills as walkers. (DS9 episodes: "Emissary", "Dax", "Equilibrium", "Facets")

History and specifics


Trill Internal Anatomy

Trill were marsupials, and as such, had abdominal pouches with which to provide incubation for their newborns. Both males and females had pouches, and both sexes were capable of incubation. The pouch was also used as a conduit for medications to quickly enter the body, as well as the joining point between host and Trill symbiont.

Tens of thousands of years ago, the bipedal Trill humanoid was covered in sleek fur and had a steeply ridged brow. It was at this stage of their evolution that the first joining occurred. (DS9 - Worlds of Star Trek: Deep Space Nine novel: Trill: Unjoined)

An important neurotransmitter in the Trill brain is isoboramine. (DS9 episode: "Equilibrium", DSC episode: "Forget Me Not")


The Trill mathematical system is noted for containing ethical modes. (TNG novel: Intellivore)

The Trill ruling council was divided into junior and senior members. Senior members, whose symbionts had lived more than one lifetime, were allowed to call general meetings. Junior members, whose symbionts had lived only one, were not. Membership was restricted to joined men until the 21st century. (DS9 short story: "First Steps")

While Trill society was sharply gendered for generations, the custom of symbionts swapping between successive male and female hosts made for an androgynous subculture. (DS9 short story: "First Steps")



Around 23,000 BC, a Trill symbiont named Sef enticed a walker to the Pool in which it lived and entered its pouch becoming the first joined Trill. (DS9 - Worlds of Star Trek: Deep Space Nine novel: Trill: Unjoined)

Two major factors contributed to the rise of Trill technology: the memories of symbionts, and easy access to ores and heavy metals. The symbionts could communicate with the humanoid Trills through joining, although the ways and means of the first jining remain shrouded in secrecy by the Trill Symbiosis Commission. Symbionts passed from host to host but retained their memories and friendships, and kept Trill society centered on a long-term view. Geologically, the planet Trill's heavy tectonic activity led to the formation of quakecaverns and eroded tunnels, through which the Trill could easily gain access to deposits of iron, aluminum, and other useful metals. The combination of the two factors led to the rapid rise of technology. (Decipher RPG module: Worlds)

As Trill society grew, their governments adopted a system influenced by the symbionts. The symbiont populations grew much more slowly than the humanoid Trill populations, so many Trills competed to have the right qualifications to be selected as a host. This general competitiveness showed through academic achievement and philosophical development—the symbionts made it clear that they would reject violent individuals who tried to become hosts by force. As a result, all Trill civilization stressed a high level of education and ethical personal responsibility. By the time they had covered all of their planet's landmasses, the Trill already had a unified world government, a meritocracy run through systems of examinations and scientific appointments. This system was well in place by the time the Trill met the Federation, but matters were still cool between the two powers. Trills valued their independence and their position as a neutral party. Over the exchange of several decades, it became clear that the Federation stood for the same high values that Trill society encouraged—and that the members of the Federation had embraced those values, due to long years of struggle and learning, having worked hard to establish what came naturally to Trill culture. Eventually, the Trill applied for and received Federation membership in one of the fastest turnaround times from application to completion. (Decipher RPG module: Worlds)


Trills have a civilization marked by a decided lack of conflict. The combination of environment taking off population pressures, crossed with the stabilizing influence of the peaceful symbionts, helped to make the Trill into intellectuals instead of warriors. Their war was not to subdue other cultures for resources, but rather to tame the environment. (Decipher RPG module: Worlds)

The Vulcans made first contact with Trill circa 2055, during the youth of Lela Dax. The highly divisive first contact "crisis" engendered many policy changes regarding the symbionts, including putting the symbiont pools under guard. The Trill government adopted a xenophobic stance, repulsing any contact with other alien species. Messages were sent to alien ships asking them to bypass the Trill system. This policy continued until the L'Dira incident in 2075. (DS9 short story: "First Steps")

By the 22nd century, Trills had largely tamed their world, and engaged in rudimentary space travel and contacts with other cultures through subspace radio. The close of the 22nd century saw the Trill invention of warp drive. By the 23rd century, Trill warp engines were on par with most Starfleet designs; Trill travelers became a common sight throughout the Alpha Quadrant, although their symbionts remained secret and the Trill had little desire to colonize or conquer other worlds. (Decipher RPG module: Worlds)

The Trill already had warp drive by the 21st century in "First Steps".

The Burn, an apocalyptic event which took place in the 31st century, greatly affected Trill. The population was decimated, and the survivors withdrew from the Federation. (DSC episode: "Forget Me Not")

Alternate timelines

In the Kelvin timeline, Doctor Leonard McCoy had a nightmare in 2255 where he had to treat streams of patients, including Trill, all by himself. (TOS - Starfleet Academy novel: The Assassination Game)

In another alternate timeline, the Trill scientist Jadzia Dax subscribed to the Bajoran religion. (SCE eBook: Lost Time)

In one permutation of the mirror universe, the Terran Empire made contact with the Trill homeworld in the 23rd century. Spock, Emperor of the Terran Empire, had all Trill symbionts in the Caves of Mak'ala killed by Captain Saavik of the ISS Enterprise, and organised the assassination of every joined Trill except for Curzon Dax. (ST - Mirror Universe novel: The Sorrows of Empire)

Known Individuals

For a list of Trill, see: Trill.


External link