Henry David Thoreau (18171862) was an American essayist, poet, philosopher, and leading transcendentalist. Best known for his masterwork Walden and his influential essay Civil Disobedience, Thoreau was a close friend and student of Ralph Waldo Emerson. His writings focused heavily on natural history, philosophy, and individual integrity. He spent two years, two months, and two days living in a cabin he built himself by Walden Pond, a formative experience that established him as a pioneer of modern environmentalism and simple living.