Patricide was the act of killing one's own father. In 2268, after James T. Kirk learned that Spock had taken command following his own injuries at the hands of Thelev, the captain was concerned, as it now made Spock unavailable to give his father Sarek the blood transfusion that would enable the life-saving surgery (a cyrogenic open-heart procedure) Sarek required. Despite Kirk's admiration of Spock's devotion to his duty, he vowed he wouldn't let the first officer commit what was, in effect, patricide. (TOS: "Journey to Babel" )