Henry Wager Halleck (January 16, 1815 – January 9, 1872) was a senior United States Army officer, scholar, and lawyer. A noted expert in military studies, he was known by a nickname that became derogatory: "Old Brains". He was an important participant in the admission of California as a state and became a successful lawyer and land developer. Halleck served as the General-in-Chief of the Armies of the United States from 1862 to 1864, and then became Chief of Staff for the remainder of the war when Ulysses S. Grant was appointed to that position.
Early in the American Civil War, Halleck was a senior Union Army commander in the Western Theater. He commanded operations in the West from 1861 until 1862, during which time, while the Union armies in the East were repeatedly defeated and held back, the troops under Halleck's command won many important victories. However, Halleck was not present at those battles, and his subordinates earned most of the recognition. The only operation in which Halleck exercised field command was the so-called siege of Corinth in the spring of 1862, a Union victory which he conducted with unnecessary caution, which allowed the Confederate force to escape. Halleck also developed rivalries with several of his subordinate generals, such as Grant and Don Carlos Buell. In July 1862, following Major General George B. McClellan's failed Peninsula Campaign in the Eastern Theater, Halleck was promoted to general-in-chief. Halleck served in this capacity for about a year and a half.
