Marc Andreessen — Birth Year: 1971

Note: The source text explicitly states Marc Andreessen was born July 9, 1971 in multiple places: in the opening description ('American businessman (born 1971)'), in the biographical information box ('(1971-07-09) July 9, 1971'), and in the main text ('born July 9, 1971'). The claim that his birth year is 1971 is directly and unambiguously confirmed by the source.