Walter "Walt" Whitman (May 31, 1819 - March 26, 1892) was an American poet, essayist and journalist. A humanist, he was a part of the transition between transcendentalism and realism, incorporating both views in his works. Whitman is among the most influential poets in the American canon, often called the father of free verse. His work was very controversial in its time, particularly his poetry collection Leaves of Grass, which was described as obscene for its overt sexuality. Walt Whitman has been claimed as America's first "poet of democracy", a title meant to reflect his ability to write in a singularly American character. A British friend of Walt Whitman, Mary Smith Whitall Costelloe, wrote: "You cannot really understand America without Walt Whitman, without Leaves of Grass... He has expressed that civilization, 'up to date, ' as he would say, and no student of the philosophy of history can do without him." Modernist poet Ezra Pound called Whitman "America's poet... He is America." Andrew Carnegie called him "the great poet of America so far". Whitman considered himself a messiah-like figure in poetry. Others agreed: one of his admirers, William Sloane Kennedy, speculated that "people will be celebrating the birth of Walt Whitman as they are now the birth of Christ".