A guard was a member of the Space Corps. When argonite pirates destroyed Space Beacon Alpha One, General Nikolai Hermack put him, Lieutenant Sorba and four other guards on the next nearest beacon, Alpha Four.
The guard reported to Sorba that he had heard a noise in the computer bay. When they found the Second Doctor, Zoe Heriot and Jamie McCrimmon, he and the other guards gave chase, but the pirates arrived, and he was gunned down by Maurice Caven. (TV: The Space Pirates)