John Hay was a writer and statesman who grew up in Warsaw, Ill., a small town about sixty miles from Clemens's hometown of Hannibal, Mo.—a common background that fostered his long friendship with Clemens. After graduating from Brown University, Hay began his illustrious career in public service as an assistant private secretary to Abraham Lincoln. Hay met Clemens in the late 1860s, and in 1871 Clemens offered Hay part ownership of the Buffalo Express, and to join him in a trip down the Mississippi to furnish material for what would appear in 1875 as the "Old Times on the Mississippi" series in the January–June and August issues of the Atlantic Monthly. Hay declined both offers. Clemens also appreciated Hay's Pike County Ballads (1871) for its verisimilitude to their boyhood region (see also SLC to John M. Hay, 6? January 1871). In 1870 Hay accepted an editorial position on the New York Tribune under Horace Greeley, and, after Greeley’s death in 1872, assisted the new editor, Whitelaw Reid. He gave up his Tribune position in 1875 and pursued a literary career as a poet, novelist, and biographer of Lincoln. Until about 1890 Hay's friendship with Clemens was lukewarm, kept up mostly through mutual friends, but their relationship changed in 1898, when Hay became secretary of state under the McKinley (and later Roosevelt) administration. Despite Clemens's anti-imperialist polemics (and Hay's support for Clemens's foe Theodore Roosevelt), their affection for each other remained solid until Hay's death in 1905 (see AutoMT1, pp. 222–24). In a 27 August 1907 autobiographical dictation, Clemens reminisced, "Hay was a man of great and varied talents and accomplishments, and was conspicuously well equipped for the several great national and international posts which he had filled in his brilliant career; and he climbed to several of them without the help of wealth, and would doubtless have climbed the rest of the way without that help, and all the public would have approved, and would also have affectionately applauded and rejoiced" (AutoMT3, p. 112).

Dr. John S. Billings served as medical inspector of the Army of the Potomac. After the Civil War he was posted to the office of the US surgeon general as a lieutenant colonel, where he established the National Library of Medicine within the War Department's Surgeon General's Library, for which he served as librarian until his retirement from active army service in 1895. In 1896 he became the first chief librarian of the New York Public Library. He was also a founding member of the Cosmos Club in Washington, D.C. He probably knew Clemens from their mutual friend Colonel George Waring, with whom Billings worked on several sanitation projects.