James Kirk's older brother, a research scientist who died with his wife on Deneva during the neural parasite infestation.
George Samuel Kirk is the older brother of James T. Kirk, who alone called him Sam. Kirk mentions him while held by Roger Korby on Exo III, noting that Sam had been planning a transfer to a research station.
In Operation -- Annihilate!, the Enterprise reaches the colony on Deneva, where Sam lived with his wife Aurelan and their son Peter. The colony has been overrun by flying neural parasites that seize control of their hosts. Kirk finds his brother already dead, and Aurelan dies shortly after describing the creatures, leaving young Peter as the surviving member of the family.