The general of the U.S.
Initally it was General Douglas MacArthur and later General Matthew Ridgeway.
General US Grant's first assignment in the US Civil War was in Missouri. In September of 1861 Grant took command of the Southeast Missouri District.
General Douglas MacArthur is the military commander who had been relieved of his command by President Truman during the Korean War, but who still had substantial support in the US public.
Most US Civil War historians are in agreement that a key determining factor in the results of a US Civil War battle was the degree that a general had in the area of command and control. This is where a general's intentions could be translated into action. The techniques of command and control at the disposal of a general could make the final results be positive or negative. If a general had a good view of the battle actions or his reporting generals did, he could alter or not alter his original plans. As an aside, this may be said to be an important factor in battles of today. The main difference now could be the power of air reconnaissance.
Brigadier General Stand Watie, Confederate Indians, CSA,and a Chief of the Cherokee Nation was the final general officer to surrender his command at the end of the US Civil War. Look at this site and you will have your answer.
Ulysses S. Grant took command of the Union Armies during the final years of the US Civil War receiving full command of the troops in early 1864. He was appointed by US President Lincoln. Grant was also given the special title of Lieutenant General. Grant has been given credit for the general that defeated the South. This had been the title of George Washington and no other US general ever had it until it was given to Grant. The Confederacy used the title of lieutenant general during the war.
Douglas MacArthur .
Union General George Wright graduated from West Point in 1822. Among the 40 graduating cadets that year, Wright ranked 24th. When the US Civil War broke out he wanted to be assigned to a command. Instead, the War Department kept General Wright in California for most of the war.
Not the military chain of command, no.
General Winfield Scott.
When the United States entered WW 1, it had an impact in the size of Allied troops. It also gave the Allies General Pershing command of most of Allied forces in the West. The US added air power to the war, and was an important factor in the end of the war in 1918.
General George B. McClellan, a major general during the American Civil War, organized the Army of the Potomac and led the Union Army as general-in-chief from November 1861 to March 1862.