Genealogy happens to be an interest of mine. In my research, I found online an alleged family tree for one of my (sourced) ancestors. Following up the tree, I got several noteworthy people, including Charlemagne. I know to take it with a grain of salt without documentation (I found a tree which has someone I'm sure is a complete fabrication), but it at least seems possible since he had 18 known kids. That reminded me of the Genghis Khan fact, and I began wondering if it had been done for other people.
I'm not necessarily interested in Charlemagne in particular or even Europe, so I welcome input from all specialties. It's okay if it wasn't a noble but just a very fertile person.
Charlemagne is the obvious candidate to bring up here. I wrote an answer looking at him here, which draws heavily on research you can read here. Now that being said, I do have a rather important correction to make here. The statistic is popularly expressed that way, but it isn't correct. 0.5 percent of the male population has a Y-Chromosome which points to a single, common ancestor from around that time, which Genghis is assumed to represent (unfortunately his name isn't on it). But this is only the Y-Chromosome, which is passed down father to father to father. To properly speaking, 0.5 percent of the male population have descended from Genghis Khan through the male line - son of a son of a son of a son. The actual number of descendants can be hypothesised as being much, much bigger, since obviously many, many, many descendants over the many generations in between, have been women! I'm not sure what the estimates are, but statistically speaking, they should be considerably higher than 0.5 percent. I don't know of specific studies of other genetic markers though.