The Klingons and the Romulans have become two ofStar Trek’smost enduring aliens, largely because their introductions onStar Trek: The Original Serieswere so great. With the premiere ofStar Trek: The Original Seriesin 1966, Gene Roddenberry introduced the world toCaptain James T. Kirk (William Shatner)and his crew aboard the USS Enterprise. Over the course of their adventures, the Enterprise encountered numerous alien species, but some stuck around longer than others. The Klingons and the Romulans both debuted as antagonists, but they have since been allies and enemies and everything in between.
Klingons and Romulans appeared inStar Trek: The Original Seriesseason 1, and they were both a major success from their very first episode.The Romulans made theirStar Trekdebut in “Balance of Terror,“which remains one of thebest episodes of anyStar Trekseries. The Klingons popped up a few episodes later, in “Errand of Mercy,” another solid episode that holds up today. While both species have changed throughout the variousTrekseries (the Klingons more than the Romulans), these episodes laid the groundwork for everything that followed.

Romulans Were Introduced In An All-Time Great Star Trek Episode
The Romulans First Appeared In TOS Season 1, Episode 14, “Balance Of Terror”
Star Trek’s “Balance of Terror” begins with the USS Enterprise investigating several Earth outposts along theRomulan Neutral Zone. They quickly get pulled into a game of cat-and-mouse with a Romulan Bird-of-Prey and its cunning Commander, portrayed wonderfully by Mark Lenard.Tension mounts as Captain Kirk and the Romulan Commander square off,trying to outthink and outmaneuver one another. While the Enterprise is faster, the Bird-of-Prey has a cloaking device, and both ships end up evenly matched. In the end, Kirk and the Enterprise emerge victorious, but only just.
Romulans Became Major Star Trek Villains After Just 2 TOS Appearances
The Romulans became one of Star Trek’s most compelling villains after appearing in only two episodes of Star Trek: The Original Series.
Mark Lenard’s portrayal of the Romulan Commander may be the biggest reason why the Romulans became such iconicStar Trekvillains. With his strategic thinking and calm demeanor,the Romulan Commander is Captain Kirk’s equal in many ways.In the end, he even laments that:“You and I are of a kind. In a different reality, I could have called you friend.““Balance of Terror” perfectly sets up the Romulans as smart and crafty foes, and establishes their connection to the Vulcans. With an introduction like that, it’s not surprising the Romulans keep coming back inStar Trek.

Klingons’ First Star Trek Episode Is Great Even Though They’ve Changed
The Klingons First Appeared In TOS Season 1, Episode 26, “Errand Of Mercy”
InStar Trek’s “Errand of Mercy,“the Starship Enterprise travels to the strategically located Organia to prevent the Klingons from taking control of the planet. Kirk tries to convince the Organians to side with the United Federation of Planets and oppose the Klingons, but they refuse to get involved in the conflict. Before long,the Klingon Commander Kor (John Colicos) arrives and declares himself military governor,while his crew of Klingons seize the planet. Although Kirk poses as a local, Kor can see that Kirk is more defiant than the others and the two go toe-to-toe.
Star Trek: Captain Kirk’s 5 Greatest Klingon Enemies, Ranked
Captain James T. Kirk went up against Klingons numerous times throughout his Star Trek career, but these five were particularly formidable.
The Organians eventually reveal themselves to be powerful incorporeal beings who singlehandedly bring a (temporary) end to hostilities between the Federation and the Klingons. LikeMark Lenard’s Romulan in “Balance of Terror,“John Colicos helped make the Klingons one ofStar Trek’smost interesting adversaries,and he and Kirk prove to be equals in many ways as well. Kor even admits that he admires Kirk, as he points out the similarities between humans and Klingons. While many things have changed about the Klingons over the years, Kor’s calm confidence and sense of honor helped inform the basis for the species.

Why Klingons & Romulans Are Still Great Star Trek Aliens 60 Years Later
Star Trek Keeps Bringing Back The Klingons & The Romulans
Both Klingons and Romulans have withstood the test of time, and remain a part ofStar Treknearly sixty years after they were first introduced.It’s almost impossible to imagine theStar Trekfranchise today without either alien species.Star Trek: The Next Generationreinvented the Klingonsand updated the Romulans, further defining what both species would become. WhileTOSwas not concerned with building aStar Trekcanon,TNGand the shows that followed built entire histories and cultures around the Klingon and the Romulan Empires.
Modern Star Trek continues to find fascinating ways to explore Klingon and Romulan culture.
FromStar Trek: DiscoverytoStrange New WorldstoLower Decks,modernStar Trekcontinues to find fascinating ways to explore Klingon and Romulan culture. Although very different, both species make compelling foils for humanity, as they have more in common with humans than they would ever admit. Thanks to Mark Lenard and John Colicos and two great episodes ofStar Trek: The Original Series, the Klingons and the Romulans have become an integral part ofStar Trekand both species have left their mark on popular culture.