The third season of Star Trek: Discovery is due to hit sometime this year, and promises some big changes for the core characters. Having spent the first two seasons in the pre-Original Series 23rd century, the next season takes place in 3187, far further into the future than any of Star Trek's previous main settings.
While this new century promises some surprises and many new faces, there are some characters from previous series in the franchise who could -and should - return to meet the Discovery crew.
Dax was one of the most popular characters on Star Trek: Deep Space Nine, and an obvious choice for a character who could be reinvented for Discovery. Dax is a member of a species called the Trill, a unique joined species made up of both human-like beings and a very long-lived invertebrate organism living in symbiosis. Certain Trill humanoids were chosen to be hosts for the symbionts, who would pass on their centuries of memories and experiences to each successive host. For most of Deep Space Nine we were in the company of Jadzia Dax, a Starfleet science officer played by Terry Farrell. For the seventh season, she was replaced by Dax's next host, Ezri, played by Nicole de Boer, providing a new slant on the character.
Showrunner Alex Kurtzmann has confirmed that we'll see a visit to the planet Trill in Discovery season three, and having a familiar Trill show up would be a brilliant way to link the new series to the period we're more familiar with. We don't know for sure how long Trill live, but Dax was already over three hundred years old during Deep Space Nine so it's not implausible that the symbiont could show up again with a new host in the far future of Discovery. Deep Space Nine rarely gets referenced in wider Star Trek, but a trailer for the new season suggests a much stronger influence, with not just the Trill but Cardassians and Lurians (Morn's people) seen as well. A new version of one of Deep Space Nine's most popular characters would cement that link.
If there's a chance Dax is returning, then it would make sense for their old friend and comrade Benjamin Sisko to return as well. Played by Avery Brooks, Sisko began Deep Space Nine as a disillusioned Starfleet officer, who got saddled with both the command of the eponymous space station and the position of Emissary of the Bajoran Prophets. These highly advanced aliens were as gods to the Bajoran people, living in a timeless realm which was accessed via the Bajoran Wormhole. Over the years, Sisko became one of the finest captains in Starfleet, protecting Bajor and the entire Alpha Quadrant and steering the Federation through one of its darkest hours. When we last saw him in the Deep Space Nine finale, he had ascended to another plane and taken his place alongside the Prophets.
Sisko's story was wrapped up nicely on Deep Space Nine, but if there was ever a time to bring him back, this would be it. By joining the Prophets he basically exists outside of time, meaning that it should make no difference to him what century he pops up in. It looks like the Federation is going through some dark times in the 32nd century, and who would be better to steer it back onto the right track? After all, he did say that someday, he'd be back.
Whoopi Goldberg's mysterious character Guinan first appeared during the second season of The Next Generation, and we only slowly learned about her past as the series continued. One thing we do know is that her people, the El-Aurians, have extremely long lifespans. Guinan was already active on Earth in the 19th century, five hundred years before her time on the Enterprise-D. A previous plan to have her appear on Star Trek: Enterprise fell afoul of that series' cancellation, but Goldberg is confirmed to be appearing on the 2021 season of Star Trek: Picard. While it's unlikely we'll see her in Discovery season three, a follow-up appearance in season four seems almost inevitable. Plus, Goldberg has aged really well, so we'd have no trouble believing she's immortal.
One character who truly timeless is Q, the near-omnipotent alien being played by John de Lancie on The Next Generation, Deep Space Nine and Voyager. Although an appearance on Picard would be the better and more obvious way to bring back the character, given his long-established antagonistic relationship with Jean-Luc Picard, there's nothing to stop him appearing in the 32nd century. Q is, after all, immortal, capable of transcending time and space and appearing anywhere and anywhen.
If de Lancie is keen to rejoin Star Trek – and his 2017 appearance in the fan series Star Trek Continues suggests he might be – then he's another character who could easily appear in both Discovery and Picard. The TNG episode “Q Who?” suggested a very interesting backstory between Q and Guinan, which still hasn't been explored. The possibility to have the two characters face off in either series is irresistible.
However, if there's one character that really deserves to return, it's the Doctor. Not the original Doctor, who was the Starship Voyager's chief medical officer throughout its seven-year run, but his backup unit. This copy was the star of the fourth season Voyager episode “Living Witness,” which saw him reactivated on a Delta Quadrant planet seven hundred years after being lost during conflict with that world. This 31st century episode was, until recently, the farthest point we'd seen of Star Trek's fictional future history. In that episode, we learn that this duplicate Doctor stayed on the unnamed planet for some years before setting off for the Alpha Quadrant.
We don't know exactly when the back-up Doctor left for the home, nor how long it would take him to reach Federation space, but it's loose enough to tie into the 32nd century setting of Discovery season three. Robert Picardo is already confirmed to be in talks to appear in Picard season two, so like Goldberg, it's not a huge stretch to imagine him also signing onto Discovery. This would allow Picardo to play two different versions of the character, who only share their first few years of memories. After that, they'd have led completely different lives, and this back-up version of the Doctor will have had all manner of adventures we'd love to hear about.