David

According to the Roman Gemellus, King David built the great temple in Jerusalem "between five and six hundred years" before the year 64. King Solomon the wise was his son, while Jesus Christ was said to be a descendant of Solomon's. (PROSE: Byzantium!)

Jewish tradition held that the Messiah would be a descendant of David and Solomon, and that he'd be born in Bethlehem. When Jesus of Nazareth fit these criteria, a small sub-sect of Judaism called Christianity was formed; they maintained that Jesus was the aforementioned Messiah, their saviour. (PROSE: Byzantium!)

According to Imperator Tannalis in the 61st century, David had extra-marital relations with a woman named Abishag. He thought he couldn't get away with a similar thing. (PROSE: Halflife)

Behind the scenes
The sculpture seen in The Girl Who Waited noticeably has the controversial fig leaf censoring David's visible penis, which is curiously only used in the Victoria and Albert Museum reproduction, effectively making the Apalapucia sculpture a reproduction of a reproduction. Even more interestingly, a sculpture with visible breasts was not only seen earlier in the episode, but focused on in dialogue.