Demosthenes was considered "the greatest of the Attic orators" of the first century BC. Demosthenes was part of a very wealthy family in Athens. When Demosthenes was young, his parents died and the family estate was left in the hands of a few guardians. The guardians had squandered the family fortune by the time Demosthenes was old enough to inherit it. At this time, Demosthenes sued the guardians in order to regain the money that they had lost. He prosecuted the case so well that people began to ask him to orate on their behalf and to provide them with counsel.
Demosthenes had many very important Athenian figures as clients. One of these was a banker, Phormio. Phormio was one of the richest men in Athens. Demosthenes won many cases for him. In one suit, the jury awarded Phormio 20 talents (approximately $10 million) after hearing only Demosthenes' argument. They didn't even bother to listen to the other side as his argument was so convincing.
Demosthenes became more involved in public affairs cases in 355 BC. He continued to prosecute private cases throughout his career, but his main interest was in public policy. In particular, he liked to deal with affairs between Athens and Macedonia. It is for these public affairs cases that he is especially remembered.
"Demosthenes." Britannica Student Encyclopedia. 2003.
"Demosthenes." Perseus Encyclopedia.