What were the main characters of the roman republic?

You have a double question here. If you mean what were the main characteristics of the Roman Republic, they were the same as any other republic, that is, every citizen had a right to vote. If you mean who were the main characters of the Roman republic, there's a long list of them. Here are a few. Lucius Brutus, the Gracchi brothers, Marius and Sulla, Cicero, Julius Caesar, Octavian. There were many more in the long history of the republic, the above are just the most famous.