The Trills , a symbiotic alien species, have become a major part of the Star Trek universe over the years. The species never appeared in The Original Series and only appeared once in The Next Generation in the episode entitled “The Host .” However, with the introduction of Jadzia Dax in Deep Space Nine , the Trills became a major focus of the Star Trek universe.
Putting a Trill on the bridge crew of a Federation space station and making them a central character meant the writers had to expand on the concept of the Trills introduced in TNG. They had to figure out all the details about Trill physiology, mentality, history, and culture. As they did, the Trill changed significantly from the species seen in the single episode of TNG.
The writers of DS9 established most of the canon related to the Trill, which was largely respected by the writers of Star Trek: Discovery when they decided to add a Trill character. However, Discovery has also decided to expand upon the Trills, adding some new details about how the species functions.
At this point, modern Trills resemble their TNG predecessors in concept only. Here’s a look at how the Trills have changed over time.
When the Trills were originally envisioned for TNG, they were both the species of humanoids that served as the hosts and the alien creatures that lived within the hosts, known as symbionts. The symbiont could only survive inside a host body, so the humanoids were basically serving the symbionts, waiting to be hosts.
The Trills in “The Host” looked vastly different than the Trills introduced in DS9. Heavy has already explored the changes to the Trills’ appearance , however, there are other physiological changes worth addressing.
In “The Host,” Odan, the original host for the symbiont, went to great lengths to avoid using the ship’s transporters. Later, he revealed that the transporter would damage the symbiont. However, in DS9, Trills had no issue with using the transporter. Since DS9 took place during the same time period as TNG, it’s unlikely that the transporter systems underwent a massive update to accommodate Trill physiology.
In the real world, DS9 writer Ronald D. Moore freely admitted that the writing team “slid by” the transporter issue when they were developing the Trills for the show. They never developed a canon reason as to why this changed. They just acknowledged that they changed it to make the species work in DS9.
“The Host” also established that the symbiont could only survive long-term in a Trill humanoid body. When Odan was fatally injured, the symbiont was transferred to the body of Commander William Riker. Though the symbiont and Riker both survived the transfer, they both started to suffer physical problems. The longer the symbiont was in a human body, the more damage was done. Eventually, the symbiont was safely transferred back into a Trill humanoid and the symbiont and Riker both recovered quickly.
DS9 established that not all humanoid Trills were physiologically compatible with hosting a symbiont, called joining. This introduced the idea that hosting a symbiont was an honor that was highly sought by compatible Trill humanoids. It also introduced the idea that there were some humanoid Trills who would never host a symbiont, which allowed the DS9 writers to explore different experiences of being Trill.
DS9 did not explicitly explore how a symbiont might join with a human host, likely because canon had established that the symbiont could only survive in a humanoid Trill. However, Discovery did choose to explore a joining between a symbiont and a human host. Gray Tal was the host of the Tal symbiont when his ship was attacked. As he was dying, Gray’s human partner, Adira, said they would take the Tal symbiont so the symbiont could survive.
Gray expressed his concern that the symbiont would harm Adira, but he realized there was no other choice. He facilitated the joining of Adira and the Tal symbiont as he lay dying. So far, Adira has not experienced any physical harm from hosting the Trill symbiont. However, they are experiencing the joining differently than previous Trill hosts. Instead of simply having the memories of the previous hosts, Adira literally sees Gray as a separate person.
When this began to happen, Gray admitted that he didn’t have any idea why Adira would be able to see him. He hadn’t heard of this happening with any other hosts. Gray posited that it was happening because Adira is human.
This is a significant change to the established canon relating to Trills that the Discovery showrunners and writers have yet to explain in detail. It’s sparked much discussion among the fandom . One of the popular theories is that the symbiont choosing the host is imperative to a successful joining. Since the Odan symbiont didn’t want to join with Riker and Riker was doing it only out of necessity, the joining didn’t work. However, since Adira and Gray both wanted the symbiont to join, the symbiont chose Adira, making their pairing successful.
Brannon Braga told the authors of Captains’ Logs: The Unauthorized Complete Trek Voyages that in TNG, the symbiont was the true “intelligence” and personality of the Trills. So, once a symbiont joined with a Trill host, the new host literally became the symbiont. The host’s memories and personality were replaced by the symbiont’s.
So, even though the physical body changed, the “person” was the same. The joining allowed the symbiont to be essentially immortal. However, the joining also meant that the humanoid host essentially ceased to exist.
According to the Deep Space Nine Companion , the DS9 writers decided to go in a completely different direction with the relationship between the symbiont and the host. Lead writer Michael Piller came up with the idea that once the host and the symbiont were joined their personalities intermingled. Piller worked intensely with veteran Trek writer D.C. Fontana to figure out how to portray these intermingled personalities in one being.
At first, they thought that Jadzia Dax’s personality would be heavily influenced by the Dax symbiont. This led them to experiment with Jadzia as a “wise old owl” in Fontana’s words. However, as they worked together, Piller and Fontana decided it would be much more interesting if the personalities of all the hosts and the symbiont were battling inside the new host.
This pivotal concept led to the current portrayal of the Trills’ personality. The humanoid host retains their own, distinct personality when they are joined with the symbiont. However, the host still gets all the memories of all the previous hosts, feels what they felt, and takes on some personality traits of the old hosts. So, the new host becomes a blend of all the previous hosts while retaining a bit of their own individuality.
Terry Farrell, who played Jadzia Dax, told the authors of The Fifty-Year Mission: The Next 25 Years that playing a Trill was always interesting and fun. She constantly got to explore new aspects of Jadzia’s personality and how it was being influenced by the Dax hosts. As an actress, that variety kept the role fresh.
The concept that Trill hosts retain their personalities and take on some of the previous hosts’ personalities was retained by the writers of Discovery. Adira’s individual personality shines through but they’re often influenced by the memories or feelings of the previous hosts. Again, the Discovery writers chose to make a significant change to the Trills when they chose to make Gray a separate entity from Adira.
Very little about the Trill culture was revealed in “The Host.” So the DS9 writers got to make up a lot of the Trill culture themselves. According to The Fifty-Year Mission: The Next 25 Years, the writers found this to be both a blessing and a curse. They had incredible creative freedom, but they also had very little guidance.
Since most of the Trill culture and societal norms were created by the DS9 team, they didn’t make too many changes. However, they did make one significant change that altered Trill culture completely. They introduced the Trill ban on “reassociation,” which prevented joined Trills from socializing with the people who were important to the previous hosts and hosts that contained symbionts who were previously important to their own symbiont. This ban especially applied to past lovers.
In the Deep Space Nine Companion, one of DS9’s regular writers talked about Piller’s decision to make reassociation illegal and a cultural taboo. He said that Piller envisioned a world where joined Trills and unjoined Trills became separate classes because the joined Trills would purposely only associate with the hosts of their symbiont’s friends. In order to prevent this societal rift, Piller decided that Trills would have a cultural taboo against reassociation.
This ban on reassociation was non-existent in TNG’s episode, “The Host.” In that episode, new hosts seeking out romantic connections with people who’d been involved with the previous host was portrayed as completely common. When Odan was transferred to a new host, they sought out Dr. Beverly Crusher to see if it would be possible to continue their relationship. However, Crusher couldn’t get over the fact that the gender of the host had changed, and she rejected Odan.
The ban on reassociation was explored in depth in the DS9 episode “Rejoined .” However, the writers didn’t always follow their own rules about reassociation. Jadzia Dax had strong, close friendships with people who had been close to the previous host, Curzon Dax.
The rules about reassociation were twisted all around for Discovery. Normally, the new host for the Tal symbiont would have to cut ties with Adira because of the ban on reassociation. However, in this case, the romantic partner of the previous host is the new host. Their continued interactions with Gray blur the lines that are supposed to exist between the previous host and the new host. It’s definitely new territory for the Trills.
Discovery also chose to make some significant changes to the Trill culture. However, those changes can easily be explained by the fact that Discovery’s Trills are from the 32nd century. In the episode “Forget Me Not ,” Adira and their crewmate Michael Burnham travel to the Trill homeworld to find answers to all of Adira’s many questions about being a host.
The Trill culture they encountered was highly suspicious of strangers and hostile toward Adira for hosting a symbiont. One of the Trill leaders explained that The Burn had wiped out nearly all of the Trill humanoids who were capable of hosting symbionts. They were concerned that the symbionts would soon run out of eligible hosts and their species would die out.
However, another species hosting a symbiont had never been successful, so they rejected the idea of a human hosting a symbiont. After Adira successfully integrated with the symbiont and gained all the memories of the previous hosts, the Trills began to accept them.
The Trill have changed significantly since their first appearance on TNG. However, the changes have made them a more complex and interesting species. It will be intriguing to see how Discovery continues to develop them in season four.