Answer:
Henry David Thoreau was a philosopher, writer, and leading transcendentalist (Transcendentalism is a philosophy that developed in New England around 1836).
Thoreau's significance is that he is best known for his philosophical and naturalist writings, one famous example being Walden where Thoreau reflects upon living simply while being in natural surroundings, which he worked on while he stayed and lived in a cabin in Walden Pond (which is in Concord, Massachusetts).