Caesar's wife a person who is required to be above suspicion.

☞ This expression comes ultimately from Plutarch's account of Julius Caesar's decision to divorce his wife Pompeia. The libertine Publius Clodius, who was in love with Pompeia, smuggled himself into the house in which the women of Caesar's household were celebrating a festival, thereby causing a scandal. Caesar refused to bring charges against Clodius, but divorced Pompeia; when questioned he replied 'I thought my wife ought not even to be under suspicion'.