Klingon
Klingons (tlhIngan in the Klingon language) are a fictional race of humanoids in the Star Trek universe. They were the main antagonists in Star Trek: The Original Series (TOS) and later became the uneasy allies of the United Federation of Planets. more...
They were introduced in the episode Errand of Mercy. Klingons were created by Gene Coon, and named for Lieutenant Wilbur Clingan, who served with Gene Roddenberry in the Los Angeles Police Department.Citation requested
In the original series the conflict between the Federation and Klingon Empire was modelled on the Cold War between the Western countries and the Soviet Union. TOS Klingons were not given many cultural traits, either original or Soviet-like, beyond a generic need for domination and tyranny. However, they were typically portrayed with a darkish skin and facial hair suggestive of Asian peoples.
With the advent of The Next Generation series and subsequent series the Klingons became an ally, and the portrayal of their culture was revised to resemble that of the Japanese Samurai (or, rather, Western imaginations of them). Klingon starship crews have also been compared to motorcycle gangs. Their cultures are centered on honour and combat. Their societies are formally governed by an emperor who has little actual power, most of which resides in highest aristocracy. They are both grouped into clans that frequently fight each other.
Klingon biology
Roughly humanoid in appearance, Klingons typically sport long manes of luxuriant hair, and for males, moustaches, and beards. Perhaps their most prominent external feature is their ridged forehead. These intricate, bony patterns vary by family line and are an evolutionary remnant of their prehistoric forms, when Klingons had a more extensive exoskeleton and a decidedly crustacean, not to say crusty, appearance.
Most body functions incorporate multiple redundancies, such as redundant stomachs, lungs, livers, an eight-chambered heart, and twenty-three ribs. This characteristic, known as "brak'lul," makes Klingons incredibly resilient. According to visual effects producer Dan Curry, Klingon ribs are arranged in a latticework; the structure might be compared to chainmail. The character Spock once said Klingons lack tear ducts, although Klingon myth states that Kahless once filled the ocean with his tears. The Klingon lifespan is at least 150 years.
Klingon females search their own partners, who they deem worthy of copulation. Normally this has to be a male of great strength, valour and at least posess great courage. The mating-process can be a very wild and sometimes violent affair. Klingon pregnancies run 30 weeks. The Process of giving birth can sometimes take days. Interbreeding is possible with humans (and they enjoy it) (B'Elanna Torres, K'Ehleyr), Romulans (Ba'el), and Trill (Yedrin Dax); Klingon traits remain dominant over several generations.
Star Trek VI: The Undiscovered Country depicts Klingons having violet blood (based on the metal ion manganese according to some unofficial sources) similar in appearance to Pepto-Bismol, but all other depictions of Klingon blood have been red, like human blood. The difference in color may have resulted from a unique atmospheric gas mix on the Klingon vessel - as suggested by the renegade boarding party's need to wear environmental suits, rather than merely wearing disguises. (The truth behind the issue is, violet blood allowed Star Trek VI to maintain a PG rating rather than something more restrictive. It also facilitates discerning Klingon blood from other species' blood without the aid of a tricorder or similar means; Colonel Worf makes this distinction during the movie's denouement.)
Human-looking Klingons
From the year 2154 until sometime after the events of Star Trek: The Original Series about a century later, Klingons had external features resembling Humans and wore their hair in a more conservative fashion than that seen later (and previously), which in actuality was because of the limited budget Gene Roddenberry had to work with. The physical changes were canonically explained in the Star Trek: Enterprise episode Divergence, where it was revealed that Klingons, who had appeared in Star Trek: Enterprise previously with the physical characteristics seen in Star Trek: The Next Generation, Star Trek: Deep Space Nine and Star Trek: Voyager were changed by a virus accidentally created when a Klingon was genetically altered in an attempt to improve the race. The genetic engineering was done using research by Dr. Arik Soong, a human. Because of this, human physical characteristics emerged before the virus eventually killed the infected Klingon. The fatal effects of the virus were halted by Doctor Phlox, however he was unable to prevent the physical changes, which would be passed on from parent to child. Presumably, by the time of Star Trek: The Motion Picture, the Klingon genes had proven stronger and eliminated the human characteristics, or the condition was cured in some other way, as human-like Klingons were no longer seen after this point.
There also appear to be two different "races" of the "original" Klingons, some who were pale with neatly groomed hair and others much darker with thick eyebrows. The two never appeared together. The differences in the two phenotypes may explain, in part, Dr McCoy's immediate lack of knowledge of Klingon anatomy when he tried to save Chancellor Gorkon in 2293.
Fan speculation
Over the decades, several non-canon novels and comic books attempted to suggest reasons for the change, including the suggestion that the human-like Klingons were a different race. The early-1990s DC Comics graphic novel, Debt of Honor suggested that the human-like Klingons were discommoded (a concept introduced in TNG). However, several Klingons who appeared human-like in Star Trek: The Original Series made appearances on Star Trek: Deep Space Nine and Star Trek: Voyager with full ridges. It has been suggested that the character of General Chang in Star Trek VI: The Undiscovered Country, whose features are less severe than other Klingons, might be a remnant of the human-like Klingons.
Read more at Wikipedia.org