The Tzenkethi are a spacefaring race from the Alpha Quadrant. Their physiology is externally humanoid, but internally quite different. Their skeleton is made up of several fluid-filled sacs, which can be contracted and expanded at will. This allows an unusual flexibility for a humanoid body. Their customary sitting position involves wrapping the legs around the main body, giving them the appearance of having been cut in half. (DS9 episode: "The Adversary", ST - Typhon Pact novel: Rough Beasts of Empire)
Tzenkethi skin tones cover the entire range of the visible spectrum, from pale green or brown, through blue, yellow and orange, to bright red and silver. Skin colours appear to correlate with an individual's function in society, with duller colours belonging to lower echelons and brighter colours to the upper echelons. Their skin is naturally bioluminescent. They have ovoid-shaped eyes, voices that sound like bells, and are described as being very tall and visually attractive to most other races, even non-humanoid ones.
Their skin carries a slight electric charge, giving other individuals a tingling sensation upon physical contact. This charge can be intensified at will to painful levels for the receiver. They are also capable of carrying and transmitting diseases to others while remaining unaffected themselves. The skin can also be used in communication. (ST - Typhon Pact novels: Rough Beasts of Empire, Brinkmanship)
Tzenkethi naming conventions involve four segments - a given name, the individual's job, their echelon, and their level of accomplishment within that echelon. The Coalition's ambassador to the Typhon Pact is named Alizome Tor Fel-A, with "tor" indicating a position as special agent to the Autarch, "fel" being her membership in the "problem-solver" echelon, and A indicating the highest proficiency in that role. These names are changeable in a given situation - for example, when Alizome dealt with the Typhon Pact she was known as Alizome Vik Tov-A, indicating a speaker of the government echelon. When she went undercover on Romulus as a trade representative, she became Alizome Nim Gar-A. She suggested to her Romulan counterpart that Tzenkethi naming conventions were a matter of privacy and mild embarrassment, although it was implied that this was a lie to cover her multiple identities.
Tzenkethi culture is based on strict classifications for all individuals. They balk at the characterisation of being a caste-based society, seeing that as implying unjustified discrimination. Rather, all Tzenkethi individuals are genetically tested while still in utero, and then assigned to an "echelon" based upon their genetic disposition. For example, individuals best suited to work in the sciences are raised in that discipline, and those best suited for diplomatic work likewise. Citizens are constantly re-tested in the course of their everyday activities. They do not see this as invasive, but rather as an opportunity to prove themselves. Movement between the echelons is possible if a citizen's regular test results suggest it would be appropriate, although the initial tests are accurate enough that it rarely happens.
Those in the lower echelons of society are not allowed to talk to those higher up unless given specific permission to do so, and then only through a complex system of gestures and honorifics. (ST novel: Brinkmanship)
Due to their physical appeal to other races, early alien contact was very traumatic for Tzenkethi, as they often found themselves kidnapped and abused. This led to a cultural discomfort with open spaces. They prefer to work in small, enclosed rooms. They use artificial gravity envelopes to make use of all surfaces within a room. It is a frequent practise for people to live and work on what humans would consider the ceiling of a room, referred to as the "superior deck," as compared to the inferior and anterior decks (the floor and walls, respectively). Using only the floor of a room is considered wasteful and uncomfortably vulnerable. They also dislike being alone, preferring the safety of crowds or areas where a lot of individuals are located. (ST novel: Brinkmanship)
The Tzenkethi homeworld is called Ab-Tzenketh, the capital planet of the Tzenkethi Coalition. The government is headed by the Autarch of the Tzenkethi Coalition, under whom serve a number of appointed ministers, or Tzelnira. (ST novel: Articles of the Federation) The palace of the Autarch is located on one of the world's moons (ST novel: Day of the Vipers). This may symbolise the strict class hierarchy among Tzenkethi (ST novel: Articles of the Federation), with the ruling caste literally looking down upon the populace on the planet below.
The full name of the Tzenkethi Autarch in 2381 was Korzenten Rej Tov-AA - "rej" being a very small category of individuals suitable to serve as Autarch, and AA indicating the best possible proficiency in that role. (ST - Typhon Pact novel: Rough Beasts of Empire) All members of society routinely praise the Autarch with ritualised gestures directed towards the moon, thankful that he is watching over them and keeping them safe. The Autarch is referred to as "My Rej" by those of lower echelons. (ST novel: Brinkmanship)
The Coalition appears to spend a great deal of its time making a scapegoat out of the United Federation of Planets, twisting all intergalactic news to make the Federation appear ruthless, dangerous and immoral. The Tzenkethi government considers the Federation's method of government dangerously chaotic - to allow all citizens of the state, however uneducated or uninformed, an equal vote in electing someone to the leadership position is unthinkable to them. On Ab-Tzenketh, only those genetically most suited to the role even have a chance to rise to such a position.
The Tzenkethi are technologically advanced; Klingon Ambassador Kage considered them capable of building metaweapons as early as 2311, also demonstrating that the Coalition was known to the Klingons and the Federation by at least this date. Tzenkethi warships are teardrop-shaped, presenting seemingly unbroken, featureless surfaces that then iris open to reveal weapons, sensors and other devices. Their planet-bound architecture uses similar principles. The Autarch's residence actually changes shape from time to time, challenging visitors each time to track down the new entrance, thus proving their worthiness to enter.
The Federation had arranged a summit on Tzenketh in 2312 (ST novel: The Fire and the Rose), but this early overture does not appear to have gone well. The Tzenkethi would later respond to the Federation's efforts to encourage trade by starting a war (ST novel: Articles of the Federation). Tzenkethi were known to raid other nation's space, and were engaged in acts of piracy in Cardassian territory as early as the 2310s. In the mid-2320s, Skrain Dukat arranged an elaborate conspiracy to fake a Tzenkethi attack on Bajor, in order to encourage the Bajorans to accept Cardassian aid. (ST novel: Day of the Vipers)
The Tzenkethi tried to invade the planet Bactrica at least three times prior to the mid-24th century. A fourth attempt was repulsed when the Bactricans appealed for intercession by the Federation. (DS9 short story: "The Music Between the Notes") The Tzenkethi and the United Federation of Planets waged war some years later. (see: Tzenkethi War)
In 2380, a two-year-old Tzenkethi named Zormonk, the son of Tzelnira Zaarok, was diagnosed with cal-tai and covertly sent into Federation space for treatment. However, the disease was too far advanced, and the child died in surgery. (ST novel: Articles of the Federation). The Tzenkethi propaganda machine was delighted to have evidence of the dead body of a Tzenkethi child in Federation hands. They insisted he had been kidnapped, and tortured in medical experiments. The Coalition recalled its ambassador soon afterwards (ST novel: Mere Mortals). Ironically, this ambassador, Emra, was actually rather forward-thinking for a Tzenkethi official and had previously attempted to open trade with Federation member worlds such as Nasat. His attitude made him unpopular, presumably why he was given the job of ambassador to the Federation, a posting the Coalition did not take seriously. (ST novel: Articles of the Federation)
The Tzenkethi government has demonstrated a willingness to secretly interfere with the other governments, even those of its allies within the Typhon Pact. They are known to have manipulated matters in the Romulan Star Empire to ensure the rise of a Praetor favorable to the Coalition's goals. (ST - Typhon Pact novel: Rough Beasts of Empire)
The Tzenkethi interfered in the internal politics of the Talarian Republic by secretly fomenting a popular revolution based on the strict gender roles of Talarian society, hoping the prevent the Republic from joining the Khitomer Accords. (ST novel: The Struggle Within)
Tzenkethi scientists experimented with creating an artificial wormhole in order to gain access to the Gamma Quadrant, which resulted in the collapse of the Bajoran wormhole. (ST novel: Raise the Dawn)
In a parallel universe, the Tzenkethi are known to have developed a form of wormhole drive, a drive even faster than quantum slipstream technology. A cruiser equipped with the drive crashed in the "main" universe, and sparked an attempt by the Breen Confederacy to gain control of it. (ST novel: Silent Weapons)