Photo colorization by Sanna Dullaway for TIME; Original image by Alexander Gardner / Library of Congress Allan Pinkerton, President Lincoln, and Maj. Gen. John A. McClernand at Antietam in 1862.

Of all the words a proud, ambitious man might use to describe himself, perhaps only Abraham Lincoln would choose strange. Yet there it is. In one of his earliest wisps of autobiography, Lincoln wrote that he was “a strange, friendless, uneducated, penniless boy” when he emerged from the backwoods in his early 20s to make his way in the world. Editors of Lincoln’s Collected Works found the word so perplexing that they added an r to transform him into a mere stranger. But the late David Herbert Donald, one of Lincoln’s most admired biographers, astutely recognized that the man meant what he said.

Strange can mean odd or quirky, and Lincoln was certainly that. His foes nicknamed him the Gorilla, which captures his long-armed, shambling animal strength. His hands and feet were enormous, and his brow was simian. Yet when he spoke, a high and reedy voice twanged forth incongruously. At one moment, he might be braying loudly over one of his own salty jokes, and at the next, lost in catatonic silence.

Strange can also mean unfamiliar, alien. This too is Lincoln, who never quite fit in. The youthful Lincoln was a rawboned genius on an uncomprehending frontier. As President, he was a self-taught rustic surrounded by the polished burghers of Eastern society. Magnetic, keenly sensitive, often able to understand others better than they understood themselves, Lincoln was nevertheless profoundly isolated. Perhaps the early deaths of his mother and sister steeped him in sorrow so thoroughly that he learned to prefer loneliness to intimacy. He “never had a confidant,” his law partner William Herndon wrote. “He was the most reticent and mostly secretive man that ever existed.”

Despite interviewing dozens of Lincoln’s associates in the months after his death, J.G. Holland, an early biographer, found himself stumped. “There are not two who agree in their estimate of him,” he wrote. One would say “he was a very ambitious man”; another would assert “that he was without a particle of ambition.” People said that “he was one of the saddest men that ever lived, and that he was one of the jolliest men that ever lived … that he was a man of indomitable will, and that he was a man almost without a will; that he was a tyrant, and that he was the softest-hearted, most brotherly man that ever lived.” The real Lincoln, Holland concluded, was the sum of his contradictions.

This shape-shifting quality has allowed writers and politicians of every stripe to claim or reject Lincoln. He has been extolled as the Great Emancipator and criticized as a racist, praised as the hero of free labor and denounced as a tool of industrialists. Lionized as a man of peace and lambasted as a warmonger, beloved for his “new birth of freedom” and berated for his offenses against civil liberties and small government. Today he is philosophical soulmate to Presidents from both ends of the spectrum: George W. Bush quoted him last year on the 10th anniversary of the 9/11 attacks, while Barack Obama name-checked him as recently as the first debate.

But his strange contradictions were essential to his political success. Though he once declared that he “was a party man and did not believe in any man who was not,” Lincoln was, in important ways, always a party of one. He had an unusual ability to look at things through the eyes of his critics as well as his friends. He was willing to turn the same cold gaze on himself, to appreciate the limits of his popularity, which he studied closely because popularity is the wellspring of power. Once, an angry critic of the confounding George McClellan demanded to know why Lincoln tolerated the Union general’s insubordinate behavior. Lincoln coolly replied that McClellan was “a majority general,” while he was but “a minority President.” That makes all the difference in a government of, by and for the people.

It is tempting in times of great political strife and division—like Lincoln’s and our own—to pine for leaders who transcend politics. But the success of the 16th President teaches that hard times are precisely when political dexterity is needed most. Politics is the machinery by which we meet tough challenges. Lincoln drilled this idea into his closest aides so thoroughly that they could channel his philosophy after he was gone. “Every war is begun, dominated and ended by political considerations,” explained John Nicolay and John Hay, Lincoln’s faithful secretaries. “War and politics, campaign and statecraft, are Siamese twins, inseparable and interdependent.”