Timothy O'Sullivan was an American photographer known for his work during the American Civil War and his contributions to early landscape photography. Born in 1840, he initially served as a photographer for the Union Army, capturing significant moments and scenes that documented the war's impact. His images provided a powerful visual record of the conflict and its aftermath. After the war, O'Sullivan became famous for his stunning photographs of the American West, particularly during the Geological Exploration of the Fortieth Parallel. His work helped to promote the exploration and settlement of the region, showcasing its natural beauty and geological features. O'Sullivan's legacy continues to influence landscape photography today.