Yiannis Kouros

Kouros dominated the longest distances for two decades. He won the 246km Spartathlon from Athens to Sparta four times, setting a course record in his first attempt in 1984 that lasted for decades, won the Sydney to Melbourne race several times, and set world bests from 24 hours to six days and 1,000 miles. His 24-hour marks lasted until Aleksandr Sorokin's era. For sheer duration, no runner has been better.