HIRAM GRANT joined the army under an assumed name, having become known as "Ulysses S. Grant" because of a mistake by the congressman who nominated him to West Point.

Grant tried to straighten out the mixup but failed, as he failed at just about everything he attempted before the Civil War, including selling firewood and collecting bills. He used the name they'd issued him under protest, but by the time he left the army after the Mexican War, he'd grown used to being U.S. Grant.

So the hero of Fort Donelson and Vicksburg came to be hailed as Unconditional Surrender Grant. Eventually he rose to four-star general -- outranking even George Washington -- and became Uncle Sam Grant, a shoo- in for the presidency.

And yet there were many who believed him to be a drunkard, a butcher and a blockhead. Sen. James Garfield, himself headed for the White House, wrote in his diary that Grant's "imperturbability is amazing. I am in doubt whether to call it greatness or stupidity."

"I'd have to say it was greatness," said James G. Barber, curator of a new exhibit at the National Portrait Gallery that marks the centennial of Grant's death.

"There are a couple of pretty reliable reports of his having been drunk on duty, in the sense that a commander is always on duty," Barber said, "but it couldn't have happened often and it never interfered with his soldiering. He hated war, which besides writing was the only thing he was good at, and he couldn't stand the sight of blood.

"As to his intelligence, you have only to read his Memoirs, which ranks with any ever written. He saw the big picture. He had profound simplicity, and great, great depth."

Profiting from the example of his father, who was a contentious windbag, Grant grew into a quiet and self-contained man who didn't complain and never answered public criticism.

In private a devoted family man and an utterly faithful friend, in public he was a stoic. He did not blush or smile when praised; neither did he bat an eyelash when told that a good friend had just been killed, or when a boy brought him the news of Lincoln's assassination. Orders and reports written on the battlefield were as clear and concise as those composed on quiet evenings in camp. One of the few times his stone face failed him was when Mark Twain made Grant guffaw at a banquet; the incomparable humorist had mastered the unconquerable general.

This plain, no-nonsense soldier became a mythic figure "because of the irresistible symbolism," curator Barber said. "There was Lee, scion of a great family of the Old South, a man who still used the f to form the double s, one of the most romantic figures of all time. Here was Grant, a product of the frontier, son of a small merchant, a man who'd struggled to make a living with his hands.

"It was the old order grappling with the new, and on the outcome rode the future of the Republic."

And war would never be the same again, because chivalry was among the casualties of Grant's style of fighting. The Fort Sumter garrison negotiated the terms of capitulation, and marched out with flags flying; when Fort Donelson's Simon Buckner tried to arrange for a stylish surrender, Grant replied curtly that "no terms except immediate and unconditional surrender can be accepted."

Gen. Buckner thought that "ungenerous and unchivalrous," especially considering that he was an old comrade-in-arms, and had lent Grant trainfare home when he'd quit the army in 1854. But they remained friends to Grant's dying day, which probably tells as much about Grant the man as anything could.

The exhibit is full of such nuggets of fact and illuminating sidelights, contained in captions that are models of graceful compression. Oddly, they give a stronger sense of the man than do the paintings and engravings, no two of which seem to show the same Grant. It was ever thus: During much of the war, major American magazines used pictures of some other guy named Grant.

The second half of the exhibit, devoted to the postwar period, is even more successful in fleshing out the enigmatic 18th president, although it seems less effective, simply because there isn't that much to say about Grant the chief executive. The American presidency was a new ballgame after the war, but Grant tried to play by the old rules. During his two terms, the government generally went to hell in a handbasket, in large part because while Grant was not a crook, some of the friends he appointed to office were.

One of his later associates swindled Grant out of all the money he had and all he could borrow, and his last years were a constant struggle to repay his debts. In his last years he redeemed both his fortune and his fame by the writing of his best-selling Memoirs, whose lucid, limpid prose betrays no sign that the author was being slowly strangled by throat cancer.

Speechless at the very end, he had to communicate through notes. His doctor pocketed them, knowing they'd be valuable. So the patient patient wrote another note that let the doctor know Grant knew what was going on, and didn't give a damn.

U.S. GRANT: THE MAN AND THE IMAGE -- Through November 11, Armistice Day, at the National Portrait Gallery.