Botanist and mechanical engineer, the most junior member of the Ares III crew. His defining characteristic is not genius but tenacity — he is smart enough to solve each problem and stubborn enough to keep solving after repeated catastrophic setbacks. His humor is not decoration; it is a cognitive survival strategy, a way of maintaining psychological coherence in conditions designed to produce despair. Watney's log voice — colloquial, profane, technically precise — is the novel's greatest formal achievement.