According to Wikipedia,
Demosthenes was a Greek statesman and orator of ancient Athens. His orations constitute a significant expression of contemporary Athenian intellectual prowess and provide an insight into the politics and culture of ancient Greece during the 4th century BC. Demosthenes learned rhetoric by studying the speeches of previous great orators. He delivered his first judicial speeches at the age of 20, in which he argued effectively to gain from his guardians what was left of his inheritance. For a time, Demosthenes made his living as a professional speech-writer and a lawyer, writing speeches for use in private legal suits.