Civil War Union Army Soldier. He is most noted for his secretly recorded lists of the dead at the infamous Southern prisoner of war camp at Andersonville, Georgia. Enlisted as a Private in Company D, 2nd New York Volunteer Cavalry on September 1, 1861, he was 18 years old when captured at Hagerstown, Maryland in July of 1863 during the Union Army's pursuit of General Robert E. Lee's Army of Northern Virginia after the Battle of Gettysburg. Sent first to Belle Island in Virginia, he was transferred to the Camp Sumter prison stockade at Andersonville, where he was assigned the duty of working in the camp's surgery as "Clerk of the Dead". Fearing the actual list would be lost or destroyed, he made a copy for himself with the hope at the end of the war to publish the list so that families would know what became of their loved ones. By the time of his exchange in February of 1865, he had recorded an estimated 13,000 names. Because the War Department misunderstood Atwater's intent for the list, it was confiscated from him, and the list was later used as evidence against Confederate Captain Henry Wirz, the prison's commander, in his trial for war crimes for which he was found guilty and hung. In July and August of 1865, Atwater returned to Andersonville in the company of Clara Barton to identify and mark the graves of the Union dead. Because of the accuracy of his list, only 460 of the graves at Andersonville National Cemetery would be marked as unknown. When the task was completed, he regained possession of the list and upon refusal to return it to the War Department he was arrested, court-martialed and sent to the Albany Penitentiary. Petitions by Clara Barton, Horace Greeley and others led to his release. His hope of publishing the list was fulfilled by Greeley on February 14, 1866. In 1868 Atwater was appointed United States Consul to the Seychelles Islands and later reassigned to the Consulate in Tahiti, where he became a dealer in pearls and a gold speculator. He married the daughter of a successful English businessman, and lived on Tahiti through the early 1900s. In 1909, he traveled to San Francisco, California for medical reasons and while there he died. At his request, his remains were returned to Tahiti where he was buried in a churchyard in the village of Papara on the southern coast. On his tombstone is the native name given to him upon his marriage - Tupuataroa, which means 'wise man'.