Captain Stewart
In the 1960s, in one universe, Captain Stewart was a member of a secretive international Intelligence Taskforce which had an office in London, with which Jenny Cornelius had contacts. Though he did not know her true nature, he was aware that she had extraordinary powers, and sometimes called her for help in a purely off-the-books capacity. Jenny treated him as a friend and also tried flirting with him with some perseverance, largely to no avail. Jenny speculated that within “ten or twenty years”, Stewart would rise in the ranks and be “a brigadier or something”. (PROSE: The Folly of Men)
Behind the scenes
Captain Stewart is implied to be a younger version of Doctor Who's Alistair Gordon Lethbridge-Stewart, who has yet to be granted his iconic rank of “Brigadier” within UNIT, the United Nations Intelligence Taskforce (just “the Intelligence Taskforce” here).
Jenny suggests that Stewart will be a Brigadier in “ten or twenty years” — that is, either in the 1970s or 1980s, taking the setting of The Folly of Men to be the 1960s. Her uncertainty is a nod to the infamous “dating controversy” about the present-day of the original run of Doctor Who serials featuring the Doctor working with UNIT: these were originally broadcast in the 1970s but with a loose premise of being set in the near future. This intent was gradually lost and, during the actual 1980s, a story was broadcast which outright treated the UNIT stories as having taken place when they were broadcast, i.e. in the 1970s.
