The Star Trek franchise's most popular aliens are arguably the Klingons, but the mythos around them can be confusing because of all the changes they have gone through over the years. Klingons have been a staple Star Trek alien ever since Star Trek: The Original Series, with their history, culture, and politics explored extensively in both the Star Trek television shows and movies. It would be hard to imagine the franchise with Klingons and the storylines they have provided.

Klingons are a warrior race who prize honor and skill in combat above everything else. They are a very tradition-bound species, with a rich history and complex ideology that revolves mostly around the mythology of their greatest historical warrior, Kahless. A Klingon's greatest honor is to die in battle, and the militaristic aspects of their culture are highly valued. Klingon culture is the antithesis of The United Federation of Planets in many ways, which made the Klingon Empire a major antagonist for Starfleet initially. As any fan will know, however, the two did manage to find common ground and become allies eventually.

Related: Star Trek Brings Back The Real Klingons Discovery Ignored

Klingons have become such a well-established species in Star Trek that it is easy to forget how different they were when they were first introduced. The species has been through many different versions and redesigns over the years, starting in TOS and going up through even the more recent Star Trek shows. Including the version first introduced in TOS, there have been five distinct varieties of Klingons over the years, making for a complicated history of Klingon development within the franchise.

Star Trek: The Original Series

Star Trek Original Klingons

Klingons were first introduced in Star Trek: The Original Series, in the season 1 episode "Errand of Mercy." The episode revolves around Captain Kirk and the crew of the USS Enterprise on a mission to the planet Organia in order to protect its inhabitants from a Klingon attack. However, it is eventually revealed that the Organians are actually quite advanced beings who don't need any protection and are simply trying to put an end to the conflict between Starfleet and the Klingon Empire. They force Kirk and the Klingon commander Kor to reconcile and predict that in the future the Federation and the Klingons will work together.

Executive producer and writer Gene L. Coon was responsible for the creation of the Klingons and based them and their culture off of both Soviet Russia and Communist China. In keeping with TOS's style of contemporary social commentary, the Klingon conflict with the Federation was supposed to represent the United States and Soviet conflict during the Cold War. This did result in some questionable makeup choices for the Klingons, with their appearance reflecting an orientalist attitude and their makeup verging on what audiences today would likely call "brownface."

Additionally, because of their inspiration, TOS's Klingons were nothing like the Klingons fans would come to know and love in subsequent shows. The biggest difference was their lack of forehead ridges, but they were also duplicitous, ruthless, and much more Fascistic, with no trace of the honor-obsessed warrior culture that would come later. Klingons would go on to appear several other times throughout The Original Series, most notably in the classic episode "The Trouble with Tribbles."

Related: Star Trek: The Klingons' Greatest Enemy Were The Tribbles, Not Starfleet

TOS Movies

Klingons featured in 3 out of the 6 Original Series movies. While only Star Trek VI: The Undiscovered Country had a plot that revolved almost entirely around the Klingons, Star Trek III: The Search for Spock featured them as a major player, and they made a brief cameo appearance at the beginning of Star Trek: The Motion Picture. The TOS film series further explored the Klingon culture and especially their relationship with Starfleet, culminating in The Undiscovered Country in which peace was finally brokered between the Federation and the Klingon Empire. This peace would set up the Klingons' return as Federation allies in later series.

Perhaps the most important thing that the TOS films did however was to give the Klingons a complete redesign. A bigger budget and vastly improved makeup techniques allowed for the creative team to make the Klingons look more alien, providing them at last with the iconic ridged foreheads. The facial hair and complexion from The Original Series were kept, but other changes were made as well, mostly to the uniform style and bizarrely the feet, which now sported a spike if the Klingon boots depicted in Star Trek 6 were any indication. The films also saw the creation of the Klingon language and the beginnings of establishing a more traditional Klingon culture. Ultimately, the TOS movies laid the groundwork for the development of the "classic" Klingons later on.

Star Trek: The Next Generation, Deep Space Nine, And Voyager

Worf Martok And BElanna Torres From Star Trek

The next three series in the Star Trek franchise greatly expanded on the Klingons, establishing their history, politics, and culture to a degree not previously seen. This began with the inclusion of a Klingon main character on Star Trek: The Next Generation. The character of Worf, who was the first Klingon to enter Starfleet, provided a lens through which to view Klingons as sympathetic. Worf introduced fans to the intricacies of Klingon culture and politics, becoming the quintessential example of the honor-obsessed Klingon warrior. Worf also went on to become a series regular on Star Trek: Deep Space Nine, and along with characters like Chancellor Gowron and General Martok, explored how the Klingon-Federation alliance held up against the threat of the Dominion War.

Star Trek: Voyager also featured a Klingon character, B'Elanna Torres, who provided a new perspective on the species through her Klingon-Human hybrid parentage. B'Elanna's struggles with both her human and Klingon sides were the crux of many of her character arcs, and her struggles to accept the Klingon half of her provided some fascinating character development. Even though Voyager was set in the Delta Quadrant, far away from Klingon space, B'Elanna's presence on the crew also led to a number of good Klingon-related storylines, most notably "Barge of the Dead" which gave fans an in-depth glimpse into the Klingon mythology around heaven and hell.

Related: Star Trek: What Happened To Worf's Son, Alexander Rozhenko

Throughout all of this world-building, Star Trek never addressed the differences between the now well-established Klingons and what they had originally been on TOS. Despite this, fans became increasingly obsessed with Klingon culture, even creating a Klingon dictionary and learn the language. TNG, DS9, and Voyager took a species that had started out as a one-dimensional enemy and shaped them into a fascinating species with limitless possibilities. This not only kept fans interested up ended up making the Star Trek universe a more complex and rich place.

Star Trek: Enterprise

Antaak From Star Trek Enterprise

Star Trek: Enterprise was the first series to offer an in-universe explanation for the differences of the Klingons from The Original Series. The Klingons in Enterprise started out looking similar to the now well-established Klingons, with long hair, full beards, and forehead ridges. Their culture and relationship with the Federation were both much different of course because of Enterprise's prequel status. Producers Rick Berman and Micahel Piller were interested in the opportunity to present a more primitive version of the Klingons and took full advantage of it, even introducing the idea of a caste system in Klingon society.

Additionally, Enterprise also sought to finally answer the question of why the TOS Klingons had no forehead ridges. They did this by introducing a storyline about a virus that almost wiped out the Klingon population. The Augment virus, as it was known, was accidentally developed by Klingon scientists when they tried to use genetically modified human DNA to create a Klingon-Human hybrid with super strength and stamina. DNA incompatibility ultimately led to death for those who were infected, but before that, one symptom of the virus was the loss of the Klingon's characteristic forehead ridges. A cure was developed by Doctor Phlox and the Klingon scientist Antaak that stopped the spread of the virus, but any physical changes that had happened before the cure was administered were permanent. This led to many Klingons who had been infected not possessing ridges.

The concept of the Augment virus as a way to explain the original Klingons was met with mixed reviews. Some fans accepted the explanation, while others found it dubious or were uninterested in any explanation in the first place. Indeed, Star Trek creator Gene Roddenberry himself stated before his passing that he didn't think there needed to be an in-universe explanation for the lack of forehead ridges in TOS. Still, the story of the Augment virus provided Star Trek: Enterprise with a couple of engaging episodes, and added another interesting layer to Klingon history.

Related: Star Trek: Why Enterprise Was Cancelled

Star Trek: Discovery

Star Trek: Discovery kicked off a new era of Star Trek shows in 2017, and Discovery's 1st season heavily featured the Klingons. However, the species underwent another dramatic redesign like they had in the TOS movies. The new design made the Klingons look even more alien, taking away their hair and giving them a larger head and more pronounced forehead ridges that extended up the entirety of their scalp. Discovery's Klingons also wore more elaborate armor and seemed more primitive and much more religiously devout.

Since Discovery seasons 1 and 2 were set about 10 years before The Original Series, some differences in the Klingons' behavior would have made sense, but their new appearance was striking and was met with heavy criticism by fans. Discovery's creative team didn't offer many explanations for the changes, although they did attempt to rectify some of them in season 2, giving the Klingons back their hair and toning down their amour a bit. Various theories and vague explanations for the change have been floating around ever since Discovery's 1st season. These include the idea of further genetic manipulation within the species or the theory that Discovery's Klingons were part of an older more traditional sect. Fans have continued to take issues with Star Trek: Discovery's depiction of the Klingons, although sentiment has mellowed somewhat now that they are no longer a major player in the show.

With Discovery season 3 making a time jump 930 years into the future, however, some fans have been speculating that season 4 might bring back the "classic" Klingons that fans know and love. Season 3 provided opportunities to see the fates of several classic Star Trek species, such as the Vulcans, Romulans, and Trill. It is reasonable to assume that season 4 might continue the idea of revisiting old species in the far future, and because of Discovery's already established Klingon connection, they would certainly be the next logical step. It is also possible that 2nd season of Star Trek: Picard will include the Klingons since Picard is the only Star Trek show to date that has not shown them at all. Whatever is in store for the Klingons in the future of Star Trek, fans will surely continue to enjoy their expanding mythos and inclusion in the canon.

More: Star Trek Can Fix Its Klingon Problem In Discovery Season 4