Henry Halleck, American lawyer, general, and scholar (d. 1872)
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.

Early in the American Civil War, Halleck was a senior Union Army commander in the Western Theater. He commanded operations in the Western Theater from 1861 until 1862, during which time, while the Union armies in the east were defeated and held back, the troops under Halleck's command won many important victories. However, Halleck was not present at the battles, and his subordinates earned most of the recognition. The only operation in which Halleck exercised field command was the siege of Corinth in the spring of 1862, a Union victory which he conducted with extreme caution. Halleck also developed rivalries with many of his subordinate generals, such as Ulysses S. 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.

Halleck was a cautious general who believed strongly in thorough preparations for battle and in the value of defensive fortifications over quick, aggressive action. He was a master of administration, logistics, and the politics necessary at the top of the military hierarchy, but exerted little effective control over field operations from his post in Washington, D.C. His subordinates frequently criticized him and at times ignored his instructions. President Abraham Lincoln once described him as "little more than a first rate clerk".

In March 1864, Grant was promoted to general in chief, and Halleck was relegated to chief of staff. Without the pressure of having to control the movements of the armies, Halleck performed capably in this task, ensuring that the Union armies were well-equipped.