Doctor Who: Flux is finally bringing back characters from the Steven Moffat era - notably Jemma Redgrave's Kate Stewart, daughter of classic character Brigadier Alistair Gordon Lethbridge-Stewart. When current showrunner Chris Chibnall took over Doctor Who, he seemed to want to make quite an abrupt break with the past. In fact, his first year as showrunner didn't even feature any classic monsters at all, with each Doctor Who season 11 episode instead introducing new threats and enemies. It meant the transition from Moffat to Chibnall was frankly rather jarring.
Since then, Chibnall has developed a rather curious relationship with Doctor Who's past. An old-school Doctor Who fan who grew up watching the classic series in the '80s, Chibnall seems much more comfortable with references to the show as it was back then - as seen by the fact his Timeless Child retcon fits with classic Doctor Who much better than it does with the post-2005 relaunch. But as time passes, he's become more confident and begun to work with the more recent lore as well. He brought back John Barrowman's Captain Jack Harkness, and Doctor Who: Flux episode 1 contained an Easter egg referencing Billie Piper's Rose, the first companion of the current era. Now, though, he's finally bringing back a Moffat-era character for Jodie Whittaker's final run.
The trailer for Doctor Who: Flux featured a blink-and-you'll-miss-it glimpse of Jemma Redgrave's Kate Stewart, one of the Doctor's key allies during the Moffat era. Daughter of Brigadier Alistair Gordon Lethbridge-Stewart, Kate had honored her father by taking over the organization he had founded, UNIT, dedicated to protecting the Earth from alien threats. Until now UNIT had apparently been disbanded in the Chibnall era, but it seems Doctor Who: Flux is correcting that mistake, because the BBC has subsequently released a promotional image featuring the UNIT logo as well. Kate Stewart is officially the first Moffat character to appear during Chibnall and Whittaker's era.
The character of Kate Stewart was originally created back in 1995, in the unlicensed direct-to-video story Downtime, that saw Nicholas Courtney reprise the role of Brigadier Lethbridge-Stewart in a battle against the Great Intelligence. Downtime explored the Brigadier's family history, and revealed he paid a heavy price for keeping the world safe - with his relationship with his daughter in particular suffering. She was played by Beverley Cressman, and became a recurring character in various Doctor Who tie-ins over the years, which explored her attempt to rebuild her relationship with her father. Moffat chose to integrate Kate into the main canon during his tenure as showrunner, revealing she had gone on to become leader of UNIT in her father's honor - although she operated under the professional name "Kate Stewart" so she wouldn't feel she was living in his shadow. He recast Jemma Redgrave in the role, meaning by now Kate should really be considered a Moffat character, reinvented for his run.
It's easy to see why Kate Stewart would appeal to Chibnall, because he'd have been following those unlicensed stories after Doctor Who was canceled in 1989. Moffat's development of the character was wonderfully organic, honoring those stories while taking her in a new direction that perfectly fitted with her past, and it's great to see Chibnall bring her back. Hopefully recurring characters like Kate will help make Doctor Who: Flux feel well-connected to everything that has gone before.