Prisms and Primates

1 Across was the seed for this puzzle.  I wasn’t sure about including 12 Across because he isn’t so well-known as he should be.   As the clue indicates, this is someone who should be considered a giant of the 20^th century, whether you agree with his politics or not.  (He was caught up in the persecution of artists by HUAC and had been an outspoken supporter of the Soviet Union.)  Check out his Wikipedia entry.

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