The nearest "ancestor of all living people" is calculated to 150 000 to 300 000 years ago, depending on which one you're talking about https://en.wikipedia.org/wiki/Mitochondrial_Eve or https://en.wikipedia.org/wiki/Y-chromosomal_Adam

https://www.scientificamerican.com/article/humans-are-all-mo...

My father researched a family tree; not rigorously, like Mormons do, but he spent about a decade tramping around the country, visiting graveyards and inspecting parish records. I have a bound volume of the tree. He claimed descent from (a) William The Conqueror, (b) Lady Godiva, and (c) Charlemagne.

I don't have his records, only the tree. The links are pretty ropey, especially when you reach further back. And he imported big chunks of it from trees built by others. His conclusions seem pretty implausible, but that article makes them seem a bit more plausible.