General-in-Chief (also known as Senior Officer of the United States Army or Commanding General of the United States Army) was the title of the highest ranked officer in the United States Army through the 19th century. At different points in US history, the title was held by all four levels of general officer.
During the Antebellum, in peacetime, the general-in-chief acted as little more than a bureaucrat. In time of war most generals-in-chief took to the field to command the US's largest army: George Washington did so in the American Revolution, Henry Dearborn did so in the War of 1812, Winfield Scott did so during the Mexican-American War, and both George McClellan and Ulysses S. Grant did so during the American Civil War. After the Civil War Generals-in-Chief usually remained in Washington, DC during the Indian Wars, the Spanish-American War, and the Philippine Insurrection, but were actively involved in crafting strategy and military policy.
In 1903 the office was dissolved with the creation of the General Staff. Ever since, the highest ranked officer in the US Army has held the title Chief of Staff of the United States Army (though since 1949 he has been subordinate to the Chairman of the Joint Chiefs of Staff).
General-in-Chief of the Confederate States Army
In the short existence of the Confederate States, the position of General-in-Chief only existed for a few months, and only one man ever held this rank. For nearly four years, President Jefferson Davis refused to create such an office, which he saw as undermining his own authority. On January 31, 1865, during the Civil War's final phase, Robert E. Lee was promoted to general-in-chief in a last-ditch effort to fend off the South's utter defeat. After barely nine weeks as chief officer of a lost cause, Lee surrendered his Army of Northern Virginia at the Battle of Appomattox on April 9. This left a vacancy in the general-in-chief position, and no successor was appointed. By the end of May, all Confederate institutions had ceased to exist.
General-in-Chief in Southern Victory
In the U.S. the general-in-chief was charged with planning overall strategy during a conflict, but at the same time, had limited supervisory authority over largely autonomous field armies. Thus, the general-in-chief's ability to carry out his duties was dependent on the cooperation of the officers under his command. This situation proved disastrous for the U.S. during both the War of Secession and the Second Mexican War. During the latter war in particular, the incumbent general-in-chief, William Rosecrans, proved completely inadequate in the face of a multi-front war against several enemies.
These inadequacies were very costly to the US in the Second Mexican War and ultimately contributed to the loss of that war. Following the war, German military observer to the US Alfred von Schlieffen suggested that the U.S. reorganize the army, with an emphasis of centralizing command by doing away with the general-in-chief position and replacing it with the much more centralized Prussian-style General Staff, with the Chief of the General Staff as the senior officer. The U.S. adopted the system.
The C.S. established the position of general-in-chief after the War of Secession. Unlike Rosecrans, General Thomas Jackson had the respect of his subordinates, and was a more talented a strategist, and so during the Second Mexican War, was extremely successful in prosecuting the war against the U.S. Nonetheless, the CSA followed the USA's lead, establishing their own General Staff and doing away with the office of general-in-chief prior to the Great War.
General-in-Chief in The Guns of the South
During the Second American Revolution (1861-1864), the position of general-in-chief of the Union Army was held first by Winfield Scott, then George McClellan, then Henry Halleck, and finally by Ulysses S. Grant. While Grant performed brilliantly and won some great battles, his leadership was no match for the Confederate Army's new repeating rifles, and he was unable to win the war.
By contrast, the Confederate States fought and won the Revolution without ever appointing a general-in-chief to lead their army. By 1868, creating such an office was still not a Confederate priority.
Other Generals-in-Chief in Turtledove's work
Other Generals-in-Chief (or an equivalent title) of the United States Army appear and are referenced as having served after the Point of Divergence in a given Harry Turtledove work. Stories set in OTL may reference past, present, and future historical senior generals, but unless their roles in the story contain speculative elements, they should not be listed here.
Douglas MacArthur is probably the Chief of Staff at the relevant Point of Divergence of Joe Steele (and its source story), but his successors are unnamed. He plays roles of varying important in "News From the Front," the Days of Infamy Series, The War That Came Early, and The Hot War, having completed his OTL tenure as Chief of Staff before the POD of either story.
George Marshall is Chief of Staff in Worldwar, until resigning in 1944 to become Secretary of State, and his successors are unnamed. In The Hot War, Marshall is Secretary of Defense, having completed his OTL generalship before the POD.
Dwight Eisenhower is Chief of Staff during The Man With the Iron Heart, and probably still holds the office at the end of the novel in 1948. Eisenhower has a direct role in The Hot War: Armistice and a background one in "Hindsight," both of which places the PODs after he had completed his tenure.
Historical Generals-in-Chief in non-chiefly roles
Certain historical Generals-in-Chief (whatever their actual title) appear in Turtledove's work in other capacities.
William Sherman plays a background role in The Guns of the South as a General, but the novel ends before his historical tenure as General-in-Chief. In How Few Remain, he has a more substantial role, but is only a Colonel as late as 1881, making any significant rise unlikely.