Most notably the make-up of the Klingons was modified for TMP. In TOS their foreheads were flat exactly like those of humans. The only distinguishing mark was their beards. In TMP and thereafter, however, the Klingons had ridges on their foreheads, to emphasize their being alien but probably also their martial nature.
With a greatly expanded budget for makeup and effects, the Klingons were completely redesigned for Star Trek: The Motion Picture (1979), acquiring ridged foreheads.
However, the Klingons seem to lend themselves to change, and each redesign was meant to make the warrior race look more menacing and alien. It's also interesting that the two biggest redesigns, Star Trek: The Motion Picture and Star Trek: Discovery, happened during the 23rd-century era.
After season 1 of TNG wrapped production, Worf's facial prosthetics were either lost or stolen. This presented Michael Westmore, TNG's primary makeup designer, with an opportunity to improve the look of the character.
The official explanation is that Klingons normally have hair but completely shave it off during a war. Pronounced. The DIS make-up includes cheek prosthetics.
In Star Trek VI: The Undiscovered Country (set around 70 years before the Next Generation era began), Colonel Worf (also portrayed by Dorn) appears as the legal advocate of Captain James T. Kirk and Dr. Leonard McCoy after they are accused of killing Chancellor Gorkon of the Klingon High Council.
Most notably the make-up of the Klingons was modified for TMP. In TOS their foreheads were flat exactly like those of humans. The only distinguishing mark was their beards. In TMP and thereafter, however, the Klingons had ridges on their foreheads, to emphasize their being alien but probably also their martial nature.
Worf is 100% Klingon by birth, although he was adopted by humans at a young age. B'elanna Torres, however was born to a Klingon mother and a Human father, so she is half Klingon, half Human.
The baldric didn't just show that Worf was Klingon. It was also an important celebration of Klingon heritage. While other baldrics might have been used to carry weapons, the Klingon ones were solely for honoring their family or house, something that was important to Worf.
Star Trek: Lower Decks season 4, episode 9 reveals that Klingons have pink blood, a departure from their usual red blood. The choice to give Klingons pink blood was made in Star Trek VI: The Undiscovered Country to create an alien look and to avoid a higher film rating.
While Klingons are normally shown to be the strongest of all species within the Star Trek franchise, they are surprisingly weak when compared to the Vulcans. This is another perfect example of how Star Trek subverts expectations, hoping time and time again that raw power is not what gives a person power.
According to the Star Fleet Medical Reference Manual, the mutual dislike between Klingons and tribbles has to do with the fact that both species have keen senses of smell, and apparently, each found the "stench" of the other extremely unpleasant. Tribbles also found food using their sense of smell.
First they said it was in the Epsilon Sagitarii system which is about 140 light-years from Earth, more recently they said it was in the Omega Leonis system 112 light years away, and in between they said it was in a fictitious system in the Beta Quadrant placing it many thousands of light years away.
The appearance of Klingons in Star Trek has evolved over time, with the original series using minimal makeup due to their tight budget. Later series introduced cranial ridges, and Discovery created a more alien look for the Klingons.
petaQ. One Klingon term used as an insult on numerous occasions was petaQ (also spelled "Pahtak", "Pathak", "p'tahk", "p'takh", "patahk", "pahtk", "p'tak", or "p'taq"). It was also used by the Klingons of the mirror universe.
The writers decided that the Ferengi ultimately failed to appear sufficiently menacing, instead replacing them with the Romulans and Borg as primary antagonists. Throughout the rest of the series, Ferengi characters were primarily used for comedic effect.
Since Pierce was dead at the time of the action, there was no way that Worf and Troi could have interviewed him. And they were shown to have slept together after their interview with him. Also Geordi states that there were no bones found, so that was part of Deanna's vision too.
Picard was under severe emotional distress, but the crew was unwilling to call him out on it - except for Worf. When he expressed his concerns to Picard, he was called a coward - a huge insult in Klingon culture. Worf became visibly angry, and told Picard he would have killed him if he had been anyone else.
Summary. Troi wore civilian clothes for most of TNG to put her patients at ease as the ship's counselor and indicate her position. Captain Picard allowed Troi to wear civilian clothes on the bridge due to her empathic abilities and his disregard for unnecessary regulations.
Worf was Married to Jadzia Dax and (spoiler) at her death in DS9 became a widower. He did have a fling with Deanna Troi through 2370, which was the result of Worf seeing himself Married to Counselor Troi in an alternate reality which led him to actually pursue Deanna romantically which was welcomed by her.
Memory Alpha notes that there is no canonical maximum estimate for Klingon lifespans, but several Klingons are known to have exceed a century, and some may have made it past 150 (earyh) years. That makes them pretty comparable to 24th century humans.
Picard replied with the phrase, "Qu'vatlh ghuy'cha' baQa'," at which point Vagh complimented him on his mastery of Klingon cursing. Qu' (task) and vatlh (hundred) make up the basis of the word Qu'vatlh (pronounced); thus, "a hundred tasks," frustration with an excessive workload and a lack of appropriate resources.
The changes are overall slight enough to be interpreted as a part of Worf's natural aging process. The make-up was not returned to the initial version of the first season for the flashbacks in TNG: "All Good Things" though.
Being descended from DNA molecules planted by the Ancient Humanoids, Klingons are distantly related to the other humanoid species of the galaxy such as Humans, Romulans and Cardassians, even though each evolved independently on their respective homeworlds.
Producers brought in a Klingon language expert to ensure the dialogue was in keeping with the fictional language created for the Star Trek: The Original Series cast's film created by Marc Okrand. The heavy makeup and the vocal effect, unfortunately, made the dialogue sound muffled by the prosthetics.
