Orator
An orator is someone who pleads a case in public. Originally, it meant speaking in a public place for or against a person or a proposal. In ancient Greek, Latin, French and English, an orator spoke for and against the accused in courts, and for or against big political decisions, such as whether to go to war. Gradually, it came to mean someone who spoke in public on formal occasions.
Oratory, or rhetoric, is the skill of argument or persuasion used by orators. The invention of printing allowed books to be multiplied and produced cheaply. This has made it possible for orators to do their persuasion in print as well as speaking. Adolf Hitler and Winston Churchill are good examples of how orators in the 20th century used media such as radio and movies where once they could only use speech. Both wrote books which sold in large numbers, though Churchill's books were about more than politics. Today television and newspapers play a vital role in deciding elections; the web less so.
Other types of orator are those who wish to change beliefs. Religious preachers like Martin Luther and John Knox changed religion in western Europe; William Wilberforce and Sojourner Truth led the fight against the evil of slavery. Emmeline Pankhurst, Martin Luther King Jr and others fought to get equal rights for all citizens.
We have orators today as much as the ancient Greeks did. The main difference is that the Greeks could see and listen to them face to face, but we rarely do today.
Rhetoric
The study of how persuasion is done by orators is called rhetoric. It has been studied for 2,500 years at least, and there are a huge number of books about it.
References
Saunders A.N.W. 1970. Greek political oratory. Penguin. Translations of some important examples.
Public speaking
Politics