Marx was a /pol/ poster of the 19th century, which is fitting because half of people on /pol/ are Russian Jews.

an excerpt of a letter Marx wrote to Friedrich Engels on July 30, 1862:

The Jewish nigger Lassalle who, I’m glad to say, is leaving at the end of this week, has happily lost another 5,000 talers in an ill-judged speculation. The chap would sooner throw money down the drain than lend it to a ‘friend,’ even though his interest and capital were guaranteed. … It is now quite plain to me—as the shape of his head and the way his hair grows also testify—that he is descended from the negroes who accompanied Moses’ flight from Egypt (unless his mother or paternal grandmother interbred with a nigger). Now, this blend of Jewishness and Germanness, on the one hand, and basic negroid stock, on the other, must inevitably give rise to a peculiar product. The fellow’s importunity is also niggerlike.

This letter, written in German, is translated and reproduced in Karl Marx, Frederick Engels, Collected Works (Moscow: Progress Publishers, 1985), pp. 388-391. It is important to note that Marx wrote the N-word in English as reproduced above; he occasionally wrote other foreign words in their original language (see the preface to the Collected Works, p. XXXVIII). The same translation appears on a Marxist website, the Marxists Internet Archive.

When he wrote the letter, Marx was angry with his democratic socialist “friend” Ferdinand Lassalle for refusing to lend him money. Lassalle was Jewish and, as far as we know, had no black ancestor.