UNIT

UNIT was a pretty steady presence in televised Doctor Who through most of the classic series, especially during the Third Doctor’s tenure. It then reappeared from time to time in the modern series, usually on the same basis: UNIT is who you go to when you need an organization that knows about aliens, and has some resources the Doctor can use: a base, equipment, transportation, connections to world governments, or even some guns and bombs, as much as the Doctor claims not to like those. Which means having a handful of recurring characters whom the Doctor knows and trusts, or at least can get along with. When you consider that these established characters presumably fight aliens when the Doctor isn’t around, that’s the perfect basis for a Big Finish spin-off. They’ve actually done this more than once, resulting in three separate eras of UNIT stories.