Ulysses S. Grant
The failed businessman who won the Civil War by refusing to stop, then spent his presidency fighting the Klan and his last year writing to save his family.

In the spring of 1861 Ulysses S. Grant was 38, working as a clerk in his family's leather goods store in Galena, Illinois, having failed at farming, at bill collecting, at real estate, and at staying in the army, which he had left in 1854 under a cloud of drinking. Four years later he accepted the surrender of the Confederacy. No American career reverses that sharply, and the reason it happened is unglamorous: Grant understood the war he was in better than the men who looked the part.
The general who kept going
His trademark appeared early. At Fort Donelson in February 1862, asked for terms, he replied that no terms except unconditional and immediate surrender could be accepted, and the initials fit. At Shiloh, beaten badly on the first day, he told Sherman that they would lick them tomorrow, and did. At Vicksburg he cut loose from his supply line, marched around the city, and took it on July 4, 1863, splitting the Confederacy along the Mississippi.
What made him decisive was a grasp of the arithmetic. The Confederacy could not replace what it lost; the Union could. So when Lincoln made him general-in-chief in 1864, Grant stopped fighting the war as a series of duels between armies and fought it as one continuous system: Sherman driving into Georgia, Sheridan burning the Shenandoah, and Grant himself locked onto Robert E. Lee in Virginia, taking appalling casualties at the Wilderness, Spotsylvania, and Cold Harbor, and refusing to withdraw after any of them. His critics called him a butcher. Over the whole war his casualty rate as a share of forces engaged was in fact lower than Lee's; the difference was that Grant kept moving forward, so the losses came all at once and in the newspapers.
At Appomattox on April 9, 1865, he gave terms of striking generosity: officers kept their sidearms, men kept their horses for the spring plowing, and no one would be prosecuted for treason so long as they went home and stayed quiet. It set the tone for a surrender that did not turn into a guerrilla war.
The presidency
Grant won the presidency in 1868 and served two terms, and for a century historians ranked him near the bottom, largely on the strength of the corruption around him, the Whiskey Ring, the Credit Mobilier scandal, a private secretary indicted, and the Panic of 1873 that wrecked the economy. He was personally honest and a poor judge of the men he trusted.
That verdict has been substantially rewritten, because it left out what he was actually trying to do. Grant enforced Reconstruction harder than any president before Eisenhower would touch civil rights. He backed the Fifteenth Amendment, signed the Enforcement Acts, and in 1871 sent federal marshals and troops into South Carolina, suspended habeas corpus in nine counties, and prosecuted the Ku Klux Klan out of existence in its first incarnation. He created the Department of Justice largely to do it. He also pursued a peace policy toward Native nations that was paternalistic and often failed in practice, but was a deliberate break from extermination. What ended Reconstruction was not Grant but Northern exhaustion, a hostile Supreme Court, and the bargain that settled the 1876 election after he left office.
The last campaign
In 1884 an investment firm bearing his name collapsed in fraud and left him penniless. Months later he was diagnosed with throat cancer. Mark Twain offered him a publishing contract on generous terms, and Grant spent his final year writing, in constant pain, often unable to speak, racing the disease. He finished the manuscript on July 16, 1885 and died a week later. The Personal Memoirs sold hundreds of thousands of sets and earned his widow roughly 450,000 dollars, and they are still regarded as the finest memoir ever written by an American soldier: plain, exact, and free of self-glorification. The man who could not make a living at anything closed his life by writing his family out of poverty in prose that has outlasted every general he beat.