Henry Wager Halleck, born in 1815 on a farm in Westernville, New York, ran away to an uncle in Utica to escape farm work and became a prodigy at West Point, teaching classes while still a cadet. He studied French fortifications in Europe, wrote an 1846 textbook on military tactics shaped by Antoine-Henri Jomini, helped write California’s constitution, and grew rich in San Francisco as a lawyer, railroad president, and quicksilver mine director. This episode follows how the man called Old Brains brought order to the Department of the Missouri in 1861 and then clashed with Ulysses S. Grant.

Halleck took credit for Grant’s victories at Fort Henry and Fort Donelson, briefly sidelined him over paperwork, and after Shiloh took personal command of 100,000 men for an advance on Corinth at less than a mile a day. P.G.T. Beauregard evacuated the town while Halleck dug in. Named general-in-chief, he acted as an adviser rather than issuing orders, and Lincoln called him a first-rate clerk. As chief of staff from 1864 he ran Union logistics, but in April 1865 he turned on William T. Sherman over surrender terms, a break Sherman made public at a Richmond review.

• Halleck married Elizabeth Hamilton, a granddaughter of Alexander Hamilton.
• His Montgomery Block was San Francisco’s first fireproof building, set on a foundation of interlaced redwood logs.
• At Corinth, Confederates ran empty trains in with whistles and cheering to suggest reinforcements were arriving.
• Sherman ordered his army to march past Halleck’s Richmond headquarters without saluting.
• Halleck helped popularize the name Alaska and died in Louisville in 1872 at age 56.