Rhetoric is one of the most famous works by one of the most famous philosophers in history. Aristotle was one of Ancient Greece's seminal thinkers, a student of Plato's and a tutor of Alexander the Great's.
Although Rhetoric seems to be a compilation of notes taken by Aristotle's students, presumably during his lectures, Aristotle is still credited as the author of the work, and he's considered the first philosopher to teach about the art of persuasion. For the reason, he's often considered the first individual to truly study it.