Gus Webber

 was a human and the chief librarian on Iwa, until the Foxes attacked, at which point he was forced to become a soldier posted at sector two. He helped the First Doctor to investigate the power drain, which they figured out was caused by Jill Helright, a telepathic child in one of Iwa's dream chambers. (PROSE: Frayed)

Behind the scenes
Since Gus spent a period of the novella helping the Doctor and asking him questions, he could be considered a companion by some.