Key events that shaped the career of writer Mark Twain include his early experiences as a riverboat pilot on the Mississippi River, which inspired his famous works. Twain's writing career began in the 1860s with short stories and humorous essays, gaining fame with "The Celebrated Jumping Frog of Calaveras County." His novels, especially "The Adventures of Tom Sawyer" and "The Adventures of Huckleberry Finn," reflect his insights on American society, race, and morality. Twain's wit, storytelling prowess, and critique of social injustices solidified his position as a central figure in American literature.