One of the advantages of being a prequel that Star Trek: Discovery enjoys is the ability to have classic Star Trek characters appear in the series. While Discovery is set roughly a decade before the voyages of Captain James T. Kirk (William Shatner) and the Starship Enterprise, a few key ancillary characters are already confirmed to appear in the series. Ambassador Sarek (James Frain), the father of Spock (Leonard Nimoy) plays a pivotal role in the life of Discovery's main character Michael Burnham (Sonequa Martin-Green), and it was just announced that the role of Sarek's human wife Amanda Grayson has been cast.
Along with Klingons and Vulcans, it didn't take long for Discovery to bring another of Trek's most popular alien species aboard. The third episode of Discovery titled "Context Is For Kings" introduced Tribbles to the show. Both as adorable mascots and, surprisingly, a scourge to be reckoned with for humans and Klingons alike, the furry little creatures have a long history throughout nearly every incarnation of Star Trek.
Tribbles are small, furry, non-intelligent life forms often mistaken for and adopted as pets. Along with their placid and non-threatening demeanor - Tribbles even lack teeth - their cooing has been known to have a tranquilizing effect on the human and Vulcan nervous systems. Tribbles also have the ability to stick to walls and vertical surfaces. Most importantly, Tribbles are asexual creatures that are essentially born pregnant, as fully half of their metabolism is devoted to reproduction. Given too much food, Tribbles begin to reproduce at a prodigious and exponential rate. A single Tribble can end up spawning a million Tribbles in just a few days if allowed to eat enough.
The fan favorite season 2 episode of Star Trek: The Original Series titled "The Trouble With Tribbles" introduced the creatures to Trek lore - though for the sake of continuity, they also appeared over a century before in the medical bay of Dr. Phlox (John Billingsley) in a second season episode of Star Trek: Enterprise. When Captain Kirk's Enterprise was assigned to guard a vital shipment of grain from the Klingons on Space Station K-7, a trader named Cyrano Jones (Stanley Adams) brought a Tribble on board the station to sell. It was purchased by Lieutenant Uhura (Nichelle Nichols), who brought it back with her to the Enterprise. Within a few days, that Tribble had spawned over a million other Tribbles, which overran both the Enterprise and the space station. However, it was the Tribbles, which died from gorging on the grain, that allowed Kirk to discover that the grain had been poisoned by the Klingons. The Enterprise crew then beamed all of the Tribbles onto the Klingon ship as it warped away.
The Klingons would eventually consider the Tribbles - which react violently to their presence - one of the great enemies of the Empire. As told by Worf (Michael Dorn) to Odo (Rene Auberjonois) when the crew of Star Trek: Deep Space Nine time traveled back to encounter Kirk's crew on K-7 in the episode "Trials and Tribble-ations," the hatred the Klingons had for Tribbles led to the Empire obliterating the Tribble homeworld in the late 23rd century. The Klingons hunted as many of the remaining Tribbles as they could across the Galaxy, causing Odo to mock his Klingon friend: "Another glorious chapter in Klingon history. Tell me, do they still sing songs of the Great Tribble Hunt?" However, the crew of Deep Space Nine ended up bringing a Tribble back with them to the 24th century, which led to their space station being swarmed with Tribbles.
Then, of course, there was the memorable Star Trek: The Animated Series episode "More Tribbles, More Troubles," in which Cyrano returns with a new breed of Tribbles that have been genetically engineered so that they don't reproduce - they just get very, very fat (it later turns out that the Tribbles still effectively, reproduce and the giant Tribbles are just colonies of smaller Tribbles all bunched together). That episode also introduced a creature called the glommer, which was created by the Klingons for one purpose: to kill and eat Tribbles.
Tribbles are fleetingly mentioned in Star Trek: The Next Generation, but they made their surprising movie debut in the Kelvin timeline of J.J. Abrams' Star Trek: Into Darkness. Late in the film, Dr. Leonard McCoy (Karl Urban) is shown testing the regenerative properties of the blood of Khan (Benedict Cumberbatch) on a dead Tribble. Khan's blood restored the Tribble back to life; McCoy then uses Khan's blood to resurrect the deceased Captain Kirk (Chris Pine).
On Star Trek: Discovery, a book titled "The Trouble With Tribbles" is on a bookshelf in the quarters of Captain Phillipa Georgiou (Michelle Yeoh) on the ill-fated U.S.S. Shenzhou as an Easter egg. In the third episode "Context Is For Kings", the Tribble appears prominently appears on the desk of the U.S.S. Discovery's Captain Gabriel Lorca (Jason Isaacs) in his Ready Room. Lorca revealed to Michael Burnham that he suffered an eye injury in the early stages of the war with the Klingons, and he has to suffer gradual adjustment to light or else lose his natural eyes (a very subtle reference to Lorca possibly having to wear an early version of the VISOR worn by the blind Lt. Commander Geordi La Forge (Levar Burton) on The Next Generation).
Given that the cooing of the Tribble calms humans, its presence could be something that helps Lorca in his recovery, or it just helps ease his burden of commanding a starship during a time of war. We also learn that Lorca collects other species for study - a skeleton of what resembles a Gorn is seen in one of the ship's labs, for instance. As Discovery is a science ship, the Tribble could be one of many species housed inside the Discovery for research. Lorca's Tribble is poised to make future appearances on Discovery, and considering there is only one on the ship (as far as we've seen), Lorca must know enough about Tribbles to avoid overfeeding it.
Since Discovery is a decade away from Kirk and the Klingons encountering Tribbles on K-7, the current crew of the U.S.S. Discovery has no way of knowing how to weaponize Tribbles against their Klingon enemy. However, as the Tribbles can't understand or communicate with humanoid species and Discovery's characters don't know what fans know of future events, there's also sadly no way to warn the Tribbles that the Klingons will blow up their home planet in just a few decades.
Star Trek: Discovery streams Sundays at 8:30pm ET on CBS All-Access in the US and on Netflix internationally.