Star Trek: Discovery is bringing back three prominent alien races from Deep Space Nine. The Star Trek franchise may have faltered on the big screen, but Star Trek: Discovery has proved to be a phenomenal success for CBS, becoming the most in-demand streaming show in the world. Season 2 ended with the USS Discovery jumping through time - meaning the show will explore the future of the Federation.
Star Trek: Discovery season 3 will be set in the year 3182, further forward in the timeline than any previous Star Trek film or TV series. Naturally, there's intense excitement about just what the galaxy will look like in 3182. The Star Trek: Discovery season 3 trailer hinted that the Federation has declined as a galactic power to just six members, although the showrunners have promised that this will be a story of hope. It's possible that the Discovery's arrival will remind the Federation what it was supposed to be about in the first place.
Interestingly, there seems to be a strong thematic link between Star Trek: Discovery season 3 and Star Trek: Deep Space Nine. The trailer includes shots of three very familiar alien races: the Trills, the Cardassians, and the Lurians. The Trills seem to be particularly important to the ongoing narrative, with showrunner Alex Kurtzman telling attendees at PaleyFest New York that "we are going to Trill this year."
The Trill were one of the most fascinating races in Star Trek: Deep Space Nine, a race of beings who are bonded to peaceful symbionts. The Star Trek: Discovery season 3 trailer appeared to show one of the caverns where the symbionts are kept prior to bonding with a host. It's possible a Discovery crew-member will be joined to a symbiont, and thus get a primer on the last few centuries' worth of galactic events. While even a Trill symbiont couldn't survive from Discovery's time to 3182, they may still be able to give enough information to help Discovery's crew - and, by extension, the viewers - figure things out.
In addition to the Trills, the Star Trek: Discovery season 3 trailer showed glimpses of Cardassians and Lurians. The Cardassians were a warlike race who served as a major antagonist in Star Trek: Deep Space Nine, and they incited a galactic conflict. It will be fascinating to see whether Cardassia has once again become a major galactic power, or whether the defeat led to a permanent decline in Cardassia's fortunes. Finally, the Lurians are a less well-known race, usually one of the background species in Quark's casino. They're rarely seen outside the Ionite Nebula region, so the brief glimpse of a Lurian may suggest that Discovery spends time in that sector of space - unless, of course, the Lurians have begun to travel more widely by 3182.