Charioteer

The highest paid athlete of all time was a Roman Charioteer named Gaius Appuleius Diocles. Over a 24 year career, he amassed a fortune worth 35,863,120 sesterces (an ancient Roman coin), or roughly $15 billion in today’s dollars. – WTF Fun Facts

Source: The highest paid athlete of all time was a Roman Charioteer; if he had lived today he would have been worth $15 billion (thevintagenews.com)