It turns out he was of mixed race – or so says wikipedia anyway
Despite Dumas’ aristocratic background and personal success, the writer had to deal with discrimination related to his mixed-race ancestry. In 1843 he wrote a short novel, Georges, that addressed some of the issues of race and the effects of colonialism. His response to a man who insulted him about his African ancestry has become famous. Dumas said:
My father was a mulatto, my grandfather was a Negro, and my great-grandfather a monkey. You see, Sir, my family starts where yours ends.