Despite his problems both on and off the golf course, Tiger Woods could still become the first athlete to earn $1 billion in his career.  Woods earned $118 million last year.

Still, Woods is not the highest paid athlete in history.

According to the University of Pennsylvania's classical studies professor Peter Struck, that honor goes to the ancient Roman charioteer Gaius Appuleius Diocles, who lived in the second century A.D. 

Struck says the illiterate racer earned "the staggering sum" of 35,863,120 sesterces (ancient Roman coins) in prize money.

"After seven savage laps, those who managed not to be upended or killed and finish in the top three took home prizes," Struck wrote.

Diocles' lifetime earnings in today's currency would come to an estimated $15 billion.

"Even without his dalliances, it is doubtful Tiger could have matched it," Struck added.