Jumping back a few thousand years to the time of Rome, Republicans were simply those who were for the Roman Republic and against autocracy. In 5th Century B.C. the Roman people threw off the shackles of the Hellenistic Etruscan Monarchs, establishing the famed Roman Republic. Until c. 80 B.C. this governmental order had never been disturbed, and wasn't again until 49 B.C. In 80 it had been Sulla, but it was temporary, in 49 it was Caesar, and it began the Roman Empire and the end of the Roman Republic.

At this stage the nation was divided, and virtually remained so for its entierety. On one side you had the Autocrats, those who supported whomever was currently wielding the powers of a Rex. On the other side you had the reactionary Republicans, who strived for nothing more than to topple the Autocrats and revive the Republic. Although not all Republicans actively sought Civil War (many of them, such as Tacitus, simply wrote), when a prominent Republican stood up, he often raised a faction of rebels and sparked yet another Roman Civil War.

The following is a list of the most notable Republicans:
Marcus Tullius Cicero
Gnaeus Pompeius Magnus
Marcus Brutus
Scipio (not Scipio Africanus)
Sextus Pompeius
Publius Cornelius Tacitus