Brian Cox OBE was a British scientist. In the early 21st century, he appeared on television, claiming that the Shakri cubes could not have been falling space debris but was uncertain if they were of extraterrestrial origin saying you would have to find someone better than himself to explain them. (TV: The Power of Three)
Brian Cox was once picked up by the Eleventh Doctor before one of his lectures, and the two traveled together for a time until the Doctor returned Brian to give his lecture, as it would inspire an audience member to take up science. (TV: A Night with the Stars)
Multi-adventures reference the rare instance when a companion is shown or stated to have multiple adventures with the Doctor but only appears in a single story.
If a medium is not mentioned, then this incarnation did not have companions who were original to that medium; it does not mean that this Doctor failed to appear in that medium.
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