The famous author known for their impact on American literature in the 19th century is Mark Twain. His novels, including "The Adventures of Tom Sawyer" and "Adventures of Huckleberry Finn", are celebrated for their rich storytelling, deep social commentary, and distinct use of dialect. Twain skillfully explored themes of race, identity, and moral dilemmas within the context of a changing America, earning him a significant place as the “father of American literature.”