Samuel Langhorne Clemens, who took the riverboat depth-sounding name of Mark Twain, was a humorist who was really funny; he was also an agnostic, lecturer and satirist, and the author of literary works widely regarded as classics today. There's an immense field of possible topics about this Mississippi-born author; it will be your loss as a student researcher and writer if you leave his pioneering work for posterity to discover.
Twain's agnostic streak ran through much of his work; "The Mysterious Stranger," among other pieces, takes savage swipes at both God and organized religion. An excellent literary research paper can track the atheistic movement in America as pioneered by Twain, researching his literary descendants in so-called "blasphemous" social commentary; a second possible topic could follow Twain's own progress in agnostic thought, especially in some of his suppressed work, just recently published.
Twain -- whose neighbor Harriet Beecher Stowe gently advocated better treatment for slaves in "Uncle Tom's Cabin" -- was far radical in his abolitionist tendencies, particularly in his classic "Adventures of Huckleberry Finn," where he satirizes racial attitudes of his time, personifying them in his leading character. A fascinating modern irony is that some commentators label Twain's satire on racism as racist. A strong research paper can compare racial commentary in Twain's day with modern times, along with critical reactions both to Twain's and Stowe's work, then and now.
Political and Social Values
Twain's satire extended far beyond abolitionism; Twain was a political satirist both in his writings and his lectures, in pieces such as "King Leopold's Soliloquy," a parody of totalitarian rule. A fruitful research paper would compare social and political value systems, including the use of political catch-phrases such as "family values," in the light of Twain's satire; how were they satirized? How do modern satirists such as Stephen Colbert and Jon Stewart continue with Twain's tradition, holding current governments up to ridicule?
Ecology vs. Man
Twain's most fundamental satire encompassed the whole of the human race; works such as "Letters from the Earth" satirize man's destruction of his fellow man and of the ecosystem. A good research paper for literature, biology or history might examine historical commentary on the ecology; how aware were commentators in Twain's day of ecological damage from the human race? Your resultant paper might prove Twain pioneered this genre of nonfiction as well.