While there are a number of fan favorite aliens in the Star Trek universe, perhaps one of the most beloved is the Trill. Made popular with the character of Jadzia Dax on Deep Space Nine, the Trill have always been a fascinating part of the Star Trek universe, and their culture has been the source of many fan discussions. With the Trill making a reappearance in Star Trek: Discovery, we’re counting down the most important legacy Trill centric episodes to watch to best understand who the Trill are, what a symbiont is, and much, much more.
"The Host" (The Next Generation, season 4 episode 23)
The Trill were first introduced in this episode, where Dr. Crusher falls in love with a Trill ambassador. However, when the ambassador is injured, he confides in Crusher that he’s carrying a symbiont and explains that while a Trill host can die, the symbiont must be protected and transferred to a new Trill host as soon as possible. Riker plays host to the symbiont until it is transferred into a new Trill. This episode plays with the idea of the symbiont being part of a host’s personality and shows how the symbiont carries the memories of each past life before it.
"Dax" (Deep Space Nine, season 1 episode 8)
Can you be blamed for something done in a past life? This first Dax-centric episode in DS9’s seven season run establishes that Jadzia remembers all things that Dax has done in the past, but questions if she can be blamed for those actions. Delving deep into the ethical quandaries of being a host, this classic episode written by Star Trek scribe D.C. Fontana is one that’s key to revisit to understand the history of the Trill, and what their culture represents. After all, as Sisko argues, Jadzia is a different person than Curzon Dax, or any of Dax’s previous lives. A current host shouldn’t have to take the fall for something done in a past life that could have happened before they were even born.
"Invasive Procedures" (Deep Space Nine, season 2 episode 4)
A Trill named Verad attacks the station and tries to take the Dax symbiont from Jadzia in this season two episode. While mostly centering on the crew’s attempts to save Jadzia and her symbiont from the invaders and take back the station, this still reveals some key points about the Trill; namely, that they don’t give symbionts to any Trill who applies and the process for application is grueling. Jadzia insists that a Trill can live a good life without being a host, but Verad is insistent that he be joined, even going so far as to force Dr. Bashir to transfer the Dax symbiont to him. Ultimately, Dax is returned to Jadzia and she is able to be joined once more with the symbiont that has become such a part of her.
"Equilibrium" (Deep Space Nine, season 3 episode 4)
When Jadzia starts having hallucinations and begins playing the same musical motif over and over, she journeys back to the Trill homeworld to understand what’s happening to her. Ultimately, at the end, it is revealed that Dax had a host she never knew about, a murderer named Joran. Joran Dax was considered to be unsuitable, and yet he was able to host the Dax symbiont without being rejected. This revealed that the process for choosing the host unfairly shut out most Trill from being able to be joined, due to the smaller number of symbionts compared to the Trill population. Sisko uses this knowledge to save Jadzia’s life, and in the end, Jadzia reconciles with Dax’s missing memories and Joran.
"Facets" (Deep Space Nine, season 3 episode 25)
“Facets” centered on a ceremony in which the previous Dax hosts were able to inhabit another’s body so that Jadzia could converse with them and learn from their experiences. This establishes that while a host can die, their memories and experiences live on within the symbiont itself, and as a result Jadzia can learn from them, even if they’re technically gone. She can also summon them to the forefront of her mind or even have them sent to others, who can then be, well, a host to the former host. The episode also features a delightfully comedic turn as Odo shares his consciousness with Curzon Dax, who’s far more relaxed than the usually stoic and buttoned up constable.
"Rejoined" (Deep Space Nine, season 4 episode 6)
Perhaps Star Trek’s most famous episode centered on LGBTQ themes, “Rejoined” sees Jadzia reunited with fellow Trill Lenara Kahn; both the Dax symbiont and the Kahn symbiont had been paired with married hosts. Jadzia and Lenara realize they have more in common now than they ever did in the past, and slowly begin to fall in love again. The episode features the first same sex kiss in Star Trek history, establishes that Jadzia is not straight, and that the Trill are a fluid species that don’t judge based on sexuality. However, due to Trill culture and taboo, Lenara and Jadzia are not allowed to be together, which makes their doomed romance all the more heartbreaking.
"Afterimage" (Deep Space Nine, season 7 episode 3)
After Jadzia’s untimely death at the hands of Gul Dukat in the season six finale, the Dax host is passed on to a new Trill, Ezri. Ezri faces uncertainty from those on DS9 who knew Jadzia, ranging from discomfort to outright hostility. This episode makes it clear that it’s difficult for a new host to pick up where their old life left off, as Ezri tries to forge her own identity in a world that’s so used to Jadzia and who she was.
"Field of Fire" (Deep Space Nine, season 7 episode 13)
It’s up to Ezri to solve a murder, with the help of past host Joran Dax. Ezri is able to summon Joran to the forefront of her subconscious and has visions of him helping her as she works to solve the murder of a DS9 crewmember. At the end of the episode, a counter-ritual sends Joran back into her subconscious, where he remains with the other Dax lives. This episode serves to show how Trill can access past lives and even interact with them, though to an outside observer they only see the current host.