Henry David Thoreau (1817-1862) was an American naturalist, essayist, poet, and philosopher. He is best known for his book Walden and his essay "On the Duty of Civil Disobedience" (originally published as "Resistance to Civil Government"). Thoreau was a lifelong abolitionist, delivering lectures that attacked the fugitive slave law while praising the writings of Wendell Phillips and defending the abolitionist John Brown. Thoreau's philosophy of civil disobedience later influenced the political thoughts and actions of such notable figures as Leo Tolstoy, Mahatma Gandhi, and Martin Luther King Jr. His writings on natural history and philosophy anticipated modern-day environmentalism.