Henri David Thoreau was an American writer, philosopher, publicist, naturalist, and poet. He prominently represented American transcendentalism throughout the mid-1800s. Thoreau’s love and observations of nature played a significant role in his writings, often forming the basis for critiques on modern society. As a naturalist, he advocated for the conservation of nature. Thoreau encouraged individual, passive, non-violent as a means of resistance to public evils. He personally supported the abolitionist movement and, as much as possible, took an active interest in the fate of fugitive slaves who were sought by the police. His essay "On the Duty of Civil Disobedience" (1849) influenced Leo Tolstoy, Gandhi, and Martin Luther King. Thoreau’s key ideas and observations are contained in these collected works.