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I read his books in Russian, haven't yet tried to read them in English. AFAIK he is not quite popular here as he is in Russia...

I don't remember all the details, but my recollection is that Jack London was once a candidate for mayor of San Francisco (Oakland???) as a Socialist. I don't know if he considered himself/was considered a Marxist as well. He was Lenin's favorite American author and was therefore widely read in Russia. Apparantly, his writing abilities kept his popularity high in the decades since.