Ghenghis Khan. He is an ancestor of over 17 million currently living humans. No one really knows how many he slept with as he was fond of raping women he found appealing in the many cities he took and kept a large harem. A historian at the time claimed he had over 20,000 children which could be true given his turnover rate of harem slaves and rape victims.
Ismail ibn Sharif wasn’t the sultan with the largest harem, but he had 800 children from a harem with eunuch guards only he could attend so he was either having the most sex of the various sultans or just had the perkiest sperm.
Fidel Castro may have been number two. He had sex twice a day with different woman one for lunch and one for dinner every year for 40 years as dictator. He would simply call it exercise.
There’s probably a lot of others.