Which U.S. general was nicknamed "Unconditional Surrender"?

In war, an unconditional surrender is a surrender in which no guarantees are given to the surrendering party. The most famous early use of the phrase (unconditional surrender) occurred during the 1862 Battle of Fort Donelson in the American Civil War. Brigadier General Ulysses S. Grant of the Union Army received a request for terms from the fort's commanding officer, Confederate Brigadier General Simon Bolivar Buckner. Grant's reply was that "no terms except an unconditional and immediate surrender can be accepted. I propose to move immediately upon your works."

Once news of Grant's victory (one of the Union's first victories) was received in Washington, D.C., newspapers stated (and President Lincoln endorsed) that Grant's first two initials, "U.S.", stood for "Unconditional Surrender," which later became his nickname. But, subsequent surrenders to Grant were not unconditional. When Robert E. Lee surrendered in 1865, Grant agreed to allow Lee's troops to go home under parole.