#1 General Horace Porter (1837-1921) was a brigadier general with the Union army during the American Civil War. Porter served as Grant's personal secretary 1869-1873 and as US ambassador to France 1897-1905. His memoir "Campaigning with Grant" was published in 1897.
#2 De Hart, Horace Porter Biddle (b. 1863) wrote as Horace Porter and wrote Our Young Aeroplane Scouts.