It is true: my great-great grandfather studied with Alexander von Humboldt. He was born in 1816 or 1817, making him a close contemporary of Karl Marx. We know that he and Marx corresponded later, as the letters have been conserved, but it occurs to me that they may have met first as students.
Humboldt was born in 1769 and was thus an 18th century person; people he met include but are of course hardly limited to Thomas Jefferson. Berlin in Humboldt’s time was a provincial town a quarter the size of Paris, and he never liked it. It is said that he was gay; look as well at this charming biography.
My ancestor remained in touch with Humboldt as well as Marx after finishing his studies and returning to Russia. He published on several topics, including the emancipation of people and second language pedagogy, in German.