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Efrosians are a species of humanoids native to the planet Efros, or Efros Delta. Members of the United Federation of Planets they are notable for their dedication to oral history, and for their musical language. Efrosians are sometimes referred to as Albino Deltans or Atreonids.

FASA's RPG book, Star Trek IV: The Voyage Home Sourcebook Update, identifies this planet as the fourth planet of the Flarset system. The alternate name "Efros Delta" is from the TTN novel Taking Wing. The use of "delta" in the name could offer an explanation why they were referred as Albino Deltans in TOS novelizations: The Voyage Home, The Undiscovered Country and VOY novelization: Flashback.
According to the RPG sourcebook Aliens, this species is called the Atreonids from Atreos IV.


Efrosians are very similar in appearance to Klingons, save for the very slight cranial ridges in comparison to a Klingon's full crest, and a copper skin complexion. Their faces contain fatty deposits inherited from their primitive ancestors who neglected to cover their faces from the harsh cold of the planet Efros. Males tend to have white or blonde hair while females usually have black or dark brown hair. It is typical in Efrosian culture for the males to grow lengthy mustaches, and most Efrosians wear their hair long. Efrosians have two stomachs and require the oils found in Levithi nuts in order to remain healthy. These nuts are found only on Efros Delta, but are exported to other Federation worlds where Efrosians live. (TTN novel: Taking Wing). Most Efrosians have weak eyes but compensate with a heightened sense of smell. Some Efrosians who are blind can correct this disability with a type of special mechanical glasses. Interestingly, despite their poor eyesight Efrosians appear to have a greater range of vision than Humans, being sensitive to a wider portion of the spectrum. (TTN novel: Sword of Damocles)

An inherent ability is their uncanny sense of direction. This is believed to have originated as a survival mechanism to deal with their world's often blinding snowstorms. As a result, Efrosians are often sought out as navigators.

Society and Culture

Cultural development

Efrosian culture is the result of living on the harsh, frozen world of Efros Delta for generations. Both technological and social development were minimal during the millennia-long ice age that ravaged the planet. Close-knit tribes formed out of a need for survival. Once the immense glaciers began to break up, the planet eventually united.

Efrosians prefer to specialize in one area of expertise.

The Efrosians do not have a written language. Although introduced to the concept by other civilizations, the Efrosian culture is still based on memorizing oral history, with libraries resembling other worlds' music archives. Furthermore, the Efrosian language is music based, which is more common among aquatic species such as the Alonis, than mammalian humanoids. (TTN novel: Taking Wing)

Efrosians lack the concept of monogamy found in many other humanoid cultures, however this lack of monogamy does not necessarily translate into sexual promiscuity. Still, Efrosians consider sexual intercourse a useful way to learn to work well with others, helping one appreciate one's colleagues. It is actually considered somewhat rude not to flirt with someone of your preferred sex. (TTN novel: Orion's Hounds) Children are raised by their mothers alone; in fact, the Efrosian word for mother is the word which translates into English as "parent". The closest term for a father is "seed-donor." Most Efrosians never meet their father. The mother is aided in caring for the child by whatever male lovers she has taken at the time. This behavior arose out of necessity; given the harsh conditions on Efros Delta, males had to mate with as many females as possible, and leaving a mother dependent upon only one male, who might not return from foraging parties, was foolish. (TTN novel: Over a Torrent Sea) (ST novel: A Singular Destiny)

Efrosians are often attuned to others' emotional needs. (ST - Destiny novel: Gods of Night). They are known as an emotionally complex people (TTN novel: Sword of Damocles)


Each tribe during the ice age had at least one warrior-priest, an individual capable of exceptional combat as well as great healing. When the ice age ended, the warrior-priests soon united Efros under a religious oligarchy led by the still-revered S'skotomz.

As members of the United Federation of Planets, an Efrosian delegation sits on the Federation Council. In 2289, Ra-ghoratreii was elected President of the United Federation of Planets and served until 2300.


Efrosians are deeply spiritual, as a rule. Their religion features the same binary morality as is found in many Earth religions. The Efrosian equivalent of heaven is known as "Endless Sky", and it is balanced by a fiery underworld. (TTN novel: The Red King) Efrosian funeral services feature a "death march" in honor of the deceased. (ST novel: A Singular Destiny). The Efrosian faith is rumored to obligate its members' names not be spoken (sung) aloud, on Efros. Nothing else is known ,because Efrosians refuse to discuss the matter with outsiders, except to mention that their religion is what enabled them to withstand the Efros ice age. Unfortunately, this has been the subject of speculation and some Tellarites believe child-sacrifice and ritual murder are common religious practices. This guarded secrecy very much remains in place in the 24th century.


Some Federation anthropologists claim there is some evidence that the Efrosians did not originally evolve on Efros. Other anthropologists suggest that the race was seeded on the planet before its ice age by the Preservers.

Unlike other planets where technology suffered under religious rule, the Efrosian warrior-priests believe technology betters life. As the climate warmed (at a very slow rate), additional energy and mineral resources were discovered that contributed substantially to their technological progress.

Prior to first contact with the Federation, the Efrosians were once under Klingon rule. However they rebelled, sending the Klingons reeling in defeat.(ST reference: Federation: The First 150 Years)

First contact was made with the Federation in 2278 when the Vulcan crew of the USS Surak visited Efros. Delighted to learn of other intelligent life, the Efrosians soon joined the Federation and began educational and philosophical cultural exchanges with other worlds. Many serve in Starfleet and the Merchant Academy as helmsmen, navigators, and medical personnel (some warrior-priests have become Starfleet doctors). (FASA RPG module: Star Trek IV Sourcebook Update)

In 2286, an Efrosian helmsman, Chitirih Ra-Dreii was aboard the USS Saratoga when it encountered the cetacean probe, along the Klingon Neutral Zone. An Efrosian ambassador was also present on Earth during the crisis. (TOS movie & novelization: Star Trek IV: The Voyage Home) An Efrosian Commander was CO of the orbiting spacedock, when hailed by the bridge simulation. (TOS video game: Starfleet Academy (SNES))

In 2293, Federation President Ra-ghoratreii granted extradition of Captain James T. Kirk and Doctor Leonard McCoy to the Klingon Empire to stand trial for the assassination of Chancellor Gorkon. Soon afterward, he handled the signing of the Khitomer Accords. (TOS movie: Star Trek VI: The Undiscovered Country)

In the 24th century, many Efrosians have protested the Integrated Officer concept in place at Starfleet Academy, due to their cultural preference to specialize in one knowledge area.

In 2377, an Efrosian male was serving as the chief mechanic of the Otamawan. He was killed by the Chalnoth bounty hunter Grauq. (DS9 novel: Warpath)

Noted Efrosians


The novelization of Star Trek VI identifies the Federation President's race as Deltan.

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