What was Mark Twains impact on american literature?

Samuel Langhorne Clemens (1835-1910), who wrote under the name of Mark Twain, became, in America, a sort of national legend, like Bernard Shaw in England. According to D.C.Browning (p.141), "[h]e was an artist in grotesque and somewhat obvious humour, his style and cadence suggesting a talker rather than a writer. He has been called 'the Lincoln of American literature'." Twain belongs in the realistic period in American Literature (1865-1900). According to Holman (p.437), "in the work of Mark Twain, of William Dean Howells, and of Henry James, the greatest contributions of the age were made." In addition, from Twain�s work, one may have a good idea of spoken language at the time.