Caesar was an honorific title for the Emperor of the Roman Empire. Julius Caesar was the first Roman to seize absolute power of the Roman state, though he refused several official titles, while his immediate successors were members of his extended family, including Augustus and Tiberius. The term "Caesar" was most commonly used in later years to refer either specifically to Julius Caesar, or in a general way to the Emperor of Rome.
In 2268, Garth of Izar compared an unspecified "Caesar" to other military leaders and despots (Napoléon Bonaparte, Alexander the Great, Adolf Hitler, Lee Kuan, and Krotus) when describing his own plans for universal conquest. (TOS: "Whom Gods Destroy")
In 2375, Dr. Julian Bashir, after expressing his disgust at the activities of Section 31, compared the Federation with a "24th Century Rome" in which laws were ignored out of a blind faith that "Caesar can do no wrong." (DS9: "Inter Arma Enim Silent Leges")