- For the video game, see Star Trek: Klingon.
- "We have always fought. We must. We are hunters...tracking and taking what we need." -- Mara.
The Klingons were a humanoid species native to the planet Qo'noS in the Beta Quadrant. They forged and ruled the Klingon Empire, one of the most prominent interstellar states over many centuries. (TOS episode: "Errand of Mercy")
The Klingon race are humanoids that stand on average at 1.6 to 1.9 meters in height and tend to have a skin tone that ranges from a swarthy olive to brown. Their hair is usually braided or worn loose and is black or dark brown in color, although some Klingons would shave their heads during times of war. Klingon hair would often turn gray or white with age. The most distinctive feature of the Klingon species are their forehead ridges which are typically unique to each individual, although family members may share similar ridge features. While externally somewhat similar to Humans, Klingons are larger and stronger than typical humans but have a much reduced tolerance of cold temperatures.
Internally, Klingon physiology contains many redundancies, when compared to other humanoids. Klingons possess eight-chambered hearts, two livers, multiple stomachs, an astounding twenty-three rib pairs, nictitating eyelid membranes, and three testicles. The duplication of vital anatomy is known as to the Klingons as brak'lul. In the field of battle these redundancies allow warriors to continue to fight even after sustaining significant injuries. (TNG episode: "Ethics"; DSC episode: "Point of Light"; TOS novels: World Without End, Dwellers in the Crucible; Decipher RPG module: Aliens; TNG novel: Debtors' Planet)
For Klingons, arsenic was a necessary part of the Klingon diet instead of the deadly poison that it was to humans. Arsenic deficiency could in fact lead to a number of health problems for Klingons. (TOS novel: Doctor's Orders)
In their history the Klingons experimented with genetic modification to further enhance themselves on several occasions, this resulted in several distinct groups of Klingons, most notably the QuchHa' which were created in the 22nd century and represented a significant proportion of the Klingon population until the late 23rd century. (ENT episodes: "Affliction", "Divergence"; VAN novel: Summon the Thunder)
- Ba'ltmasor Syndrome
- Ka'Hat plague
- Klingon augment virus
- Mach ghotI'
- T'Viad's syndrome
Klingon culture was shaped by centuries of tradition. Most of the basics of their society were laid out by Kahless the Unforgettable during the forging of the First Empire. (DS9 episode: "The Sword of Kahless")
The Code of Kahless consisted of basic rules to limit combat to a contest between equals. It ensured Klingons remained true to their word, that they would not intentionally target non-combatants, or declared neutral parties, and that they would attack openly, and not hide behind poisons or assassins. It also ensured that Klingon warriors would fight for their families and houses, not just for themselves, providing the foundations for a stable Klingon civilization. While for periods of Klingon history the Code had been distorted, or largely ignored, it had never been entirely forgotten, and ensured at least some semblance of Klingon unity. 
According to Klingon belief, the honored dead served Kahless the Unforgettable in Sto-Vo-Kor, where, according to some tradition, they serve in the Black Fleet, battling one another in a constant cycle of glorious battle, interspersed with great feasts and the singing of songs and tales of battle. (VOY episode: "Barge of the Dead"; GKN novels: A Good Day to Die, Honor Bound)
The dishonored, however, were banished forever to the fire and icy wastes of Gre'thor, a barren wasteland guarded by the great Fek'lhr beast, the Klingon devil. When a dishonored Klingon died, they would not appear in Gre'thor at once but would have to make the journey to this darker aspect of the afterlife. Once a Klingon arrived in the underworld, they would board the Barge of the Dead, where Kortar, the first Klingon, would set sail for Gre'thor. On the journey there are many dangers, such as the Kos'karii, who attempt to lure warriors into the water with their siren-like voices so that they would be lost forever. (VOY episode: "Barge of the Dead")
Another aspect within Klingon lore was the demon Shadowheart who attempted to usurp the position of the Klingon devil but was defeated. However, his actions earnt the respect of the Klingon devil who made Shadowheart the master of shadows in the mortal world. Klingons were known to be disheartened when they hear the name Shadowheart with infants being taught to look at the shadows through the corners of their eyes because if they saw a demon then it was that perons's day to die. (TNG comic: "Shadowheart")
Ancient Klingon belief stated that their race were created by the Old Gods. The first member of their race was Kortar. He was alone, which saddened him, so the gods created a second female Klingon heart. The two battled and the female Klingon warrior defeated Kortar, but instead of slaying him, she proposed that they mate for together they were more powerful than anyone. The two then destroyed the Klingon gods because "they were more trouble then they were worth". This history would be symbolically repeated in Klingon weddings well into the 24th century. (DS9 episodes: "You Are Cordially Invited", "Homefront")
Klingon marriage ceremonies were designed to emulate the original marriage made between Kahless and the Lady Lukara, and the myth of the first marriage in Klingon society of Kortar who mated with the first Klingon woman and destroyed the gods that created them. In the ceremony, the groom would be accompanied by the Tawi'Yan, the sword bearer, who's function was similar to that of the best man in Human weddings. These individuals carried fake clubs to represent the soldiers of the tyrant Molor who came to kill Kahless and the Lady Lukara moments after they were married. (DS9 episode: "You Are Cordially Invited")
- "When threatened, fight." -- Klingon phrase.
The Klingon species are highly aggressive and are known to fight for almost any reason but typically do so when honor is at stake. Due to their nature as predators, any form of suspicious behavior from whispering to weakness can set off their warrior instincts. Conflicts such as insults to their honor, injustice, a difference in opinion or a crime can only be resolved through violence. As such, Klingons do not shirk from combat and backing away from such confrontations is seen as a sign of cowardice.
The race's warrior mind means that they prefer matters to be clear-cut with speech as well as manners being blunt - this means that they ignore ambiguous concepts as there should be no misunderstanding. To the Klingon psyche, things are either black or white, good or evil - there is nothing in-between the two. This means that a warrior must declare his intent and say what's on his mind. They do this proudly and look into the eyes of others as not doing so is insulting.
Klingon lifestyle means that all utilities must have a purpose and be worthwhile. Things whose purpose are not immediately apparently are scoffed at and ignored. This has resulted in luxuries or comfort being almost completely ignored by the Klingon people who do not make use of recreation in the form of holo-programs or mattresses. Comfort is not something a warrior takes part in. Even their exercise takes this into account with an element of real danger being present in order to make it worthwhile. This means that rituals must test the strength of a warrior while songs must tell the deeds of great warriors and battles.
Despite all this focus on combat, the teachings of Kahless enforced the concept of honor within Klingon lives which makes it the most important aspect within their society. This means that the total sum of their actions as well as those of their parents are considered. This can be gained through victory and sacrifice or lost through shame and defeat. This means that a Klingon will need to satisfy their honor and avoiding such an action means that they will lose face. (Decipher RPG module: Aliens) Despite this being the case, during war time, the great honor Klingons can achieve is victory which means that they are capable of deceptive actions such as waiting in ambush for their enemies. (DS9 episode: "The Way of the Warrior")
Klingon culture was shaped around the following of the K'ajii, the Warrior Path. (ST novel: The Return) This means that every Klingon wants to grow up to be a warrior which has resulted in the prominence of the warrior caste. However, with so many recruits there exists few positions to fill the demand as every individual seeks to gain entry into the best Klingon academy. At graduation, the Klingon petitions his house for warrior status which is a prideful act. However, those that do not reach such positions within their lives are expected to find other means to support themselves as well as their houses through some other lower profession such as being a factory worker, farmer or a merchant.
In addition to this, Klingon society is divided into numerous tiers with the nobility being the highest. These are the lords of the houses whether they are Great or minor ones and possess a great deal of power through the armies as well as lands under their command. Due to their status, they are presumed to be the most honorable of their kind and enjoy a great deal of privilege. The second tier consists of those who seek the warrior's path by admission into the military though this is not a hereditary position as that of the nobility. However, relations to a loyal warrior counts in the applicant's favor. The tier below the warriors consists of accountants, weapon-smiths, nursemaids as well as other second-rate professions which are required to maintain their society. As mentioned earlier, this consists of those Klingons that were refused induction into the military though some decide to follow the family business instead. The second lowest tier consists of the subjugated races within the Klingon Empire who possess a ranking greater then a slave but lower then an actual citizen. At the very bottom of Klingon social structure consists of those who have suffered from discommendation and were banished from the Empire. (Decipher RPG module: Aliens)
Klingon culture was often brutal and extremely violent. Duels to the death over trivial insults were commonplace, and vendettas between various Klingon families could often result in virtual all-out war. In combat, the Klingons were unyielding, refusing to withdraw or retreat even against unwinable odds. Surrender was not an option for a Klingon warrior. 
Klingons enjoyed life to the full, each victory in battle was celebrated with great feasts, and even defeats are celebrated in songs and stories. The experience of battle was often as important as a victory. 
The loyalties of Klingons were generally first to their family, then to their house, and finally to the Empire. When the goals of the High Council and the goals of their house were in conflict, Klingons would invariably support their family and close allies over their government. 
The belief in combat was prevalent in the behavior of all Klingons, influencing the behavior of Klingons. For example, a strike against a fellow warrior with the back of the hand was considered a challenge to the death. Honor was valued, and deceit and deception despised by Klingon; Klingons spoke proudly to one another with a loud voice, hushed whispers were considered insulting, as was standing far away from the person being spoken to. This bold sense of honor was likely the source the Klingons animosity for the Romulans, who were famed for working in the shadows. (DS9 episode: "Apocalypse Rising")
In a sense, most Klingons were profoundly selfish, willing to waste the Empire's resources in a futile battle, if it ensures the glorious death they look forward to. This pursuit of honor at the cost of more tangible goals has cost the Empire dearly in the past. Indeed Klingons were somewhat obsessed with combat. Famous warriors were revered the way artists, scientists, or statesmen were on other worlds. Almost the entire Klingon economy was devoted to financing the massive Klingon war machine, and the most influential families maintained their own private armies, to ensure they could engage in warfare even if the government could not. It is thus not surprising that the Empire has clashed with all its neighbors multiple times during its history, nor that civil war breaks out with almost every generation on Qo'noS. 
Klingon culture is defined by and full of ritual, these include: The Age of Inclusion, Ak'voh, Brek'tal ritual, Bre'Nan ritual, Day of Honor, Challenge of Spirit, Discommendation, Hegh'bat, Ja'chuq, Kal'Hyah, Kot'baval festival, Mauk-to'Vor, Muar'tek Festival, Plea for the Dead, Rite of Ascension, Rite of Blood Peace, Rite of MajQa, Rite of Succession, Rite of Vengeance, R'uustai, Sonchi ceremony, SonchIy ceremony and Ya'nora kor.
Klingon recreational activities include the B'aht Qul challenge, Baqlaq and Qa'vak.
Foods and drink
Klingon cusine included: mot'loch, chech'tluth, heart of targ, persaba fruit, rokeg blood pie, bregit lung, sour tea, khizr, Qagh, krada legs, minn'hor cheese, durani lizard skins, bahgol, gagh, racht, zilm'kach fruit, pipius claw, grapok sauce, gladst, whitefang steak.
While humans could consume most Klingon foods and beverages safely, there were other dishes that were not safe for humans to consume. Consumption of those dishes could lead to illness or death for humans. Some Klingon dishes contained arsenic, which was poisonous for humans but a necessary part of the Klingon diet. Klingon tea was quite poisonous to humans without the antidote being readily available and even Klingons had difficulty digesting the tea once consumed. Otherwise, as Doctor Katherine Pulaski once noted, "What kills us, kills them" when it comes to poisonous foodstuffs. (TOS novel: Doctor's Orders; TNG novel: Debtor's Planet; TNG episodes: "Up the Long Ladder", "A Matter Of Honor")
Perception by others
The Romulans initially referred to Klingons as Khell'oann-mhehorael, a pejorative term which meant "more of them, from somewhere else", referring to the Klingons' place as the second major alien species targeted by Romulan militarism. Since the initial contact, the word tlhIngan has been Romulanized as, "Kll'inghann." (TOS novel: The Romulan Way)
Some Cardassians referred to Klingons disparagingly as "the Foreheads". While their warrior reputation made the Founders consider the Klingons as the Alpha Quadrant's version of the Jem'Hadar and thus something they wished to shape into servants within the Dominion. (DS9 novel: Vengeance)
List of common weaponry
- Bat'leth (mid-range)
- Chon'naq (mid-range; literally, "Belly-spear")
- Disruptor (long range)
- D'k tagh (short range)
- Gin'tak (mid-range)
- Haf'leth (mid-range)
- Iw'taj (short range; literally, "Blood-knife")
- Jej'taj (short/long range)
- Kligat (long range)
- Mek'leth (short range)
- Mevak (short range)
- Oy'naq (mid-range; AKA painstik)
- Qut'luch (short range)
- Tik'leth (short range; literally, "Long sword")
- See main article: Klingon history.
- See main article: Klingonese.