For Henry Louis Gates Jr., the challenge of making a documentary about Abraham Lincoln was daunting but ultimately too good to pass up.

The only question was, which Abraham Lincoln?

“I got this reading list, and every book I read had a different Lincoln in it,” says the Harvard University history professor by phone from Washington, D.C.

There was Lincoln the Great Emancipator, Lincoln the White Supremacist, Lincoln the Martyr, Lincoln the Tyrant/War Criminal, Lincoln the Romantic Lover, the Melancholic, the Atheist, the Orator, the Opportunist, the Gay, the Hero of Fidel Castro. . . . “And ultimately Lincoln the Unknown,” Gates summarizes. “I thought it could be fun, without even using the word, to do a postmodern Lincoln.”

That’s the Honest Abe (or one of them) who emerges in “Looking for Lincoln,” the lively, intriguing two-hour PBS documentary that airs at 9 p.m. Wednesday on KCET. Written and presented by Gates, “Looking for Lincoln” leaves no stovepipe hat unturned in its search for the prismatic 16th president. Although, or perhaps because, he is the most written-about of America’s chief executives, Lincoln remains something of an Rorschach blot. His Mt. Rushmore-sized legacy rests on the fault lines of the nation’s most painful and complex themes and leitmotifs: slavery, black-white relations and the sometimes precarious balance between states’ rights and federal unity. Gates, who grew up in Piedmont, W.Va., learning to rote-idolize Lincoln, was no exception. But as he dug deeper into his research, he unearthed a number of jarring insights. “All of a sudden I find out Lincoln used the ‘N’ word, Lincoln liked ‘darky’ jokes, Lincoln liked minstrel shows.”

In “Looking for Lincoln,” being shown to coincide with the bicentennial of its subject’s birth, Gates fittingly begins and ends his meditations at the Lincoln Memorial in Washington. In between, he attempts to carve through the monumental marble icon and discover the flawed, flesh-and-blood human within.

During his odyssey, he receives assistance from historians Doris Kearns Goodwin, David Herbert Donald, and Harold Holzer; former Ebony magazine editor Lerone Bennett; former Presidents George W. Bush and Bill Clinton; historical reenactors; and a number of ordinary Americans. “Lincoln is a composite of all these images that people see refracted and reflected inside themselves,” says Gates, who specializes in African American history and literature. “He is the mirror of the American soul.”

Gates acknowledges that looking for Lincoln required some soul-searching of his own, as a historian, an American and an African American. In the documentary, he quickly takes aim at what may be the most sensitive aspect of Lincoln: his attitudes about race.

In reality, Gates says, this discussion comprises three “sub-discussions”: one on race and slavery, a second on racial equality and a third on colonization. “My metaphor is like braiding hair.”

Although Lincoln found the institution of slavery morally abhorrent, he didn’t believe that blacks and whites were equal. He probably would’ve been appalled at the idea of an African American becoming president, an awkward twist considering that so many prominent politicians, civil rights leaders and other Americans regularly invoke his name as the patron saint of their righteous causes.

“He’s certainly my favorite president,” Gates says. “He’s George Bush’s favorite. And, my God, Barack Obama has adopted him as his father.”

Lincoln at various times advocated shipping blacks to Africa or Panama. “Whereas abolition was part of his moral compass, equality was not,” Gates says. It was pragmatism, more than dawning enlightenment, that finally drove him to write the Emancipation Proclamation. “The irony of Abraham Lincoln is that he changed,” Gates says. “He changed for two reasons. One is that he met Frederick Douglass [the venerable abolitionist, reformer and newspaper publisher]. And he decided that he needed black troops to win the war.”

But it was only with the adoption of the 13th Amendment several months after Lincoln’s assassination that slavery was formally abolished (in law, if not fully in practice). And despite the amendment’s passage and the mixed results of Reconstruction, three more generations of racial apartheid would persist in the South in the form of Jim Crow.

Gates also learned that Lincoln, like many whites in his day, apparently never sat down to a meal with a black person or spent an entire day in one’s company. Those facts typically were bowdlerized from the official hagiography that took shape practically from the instant that Lincoln was shot on Good Friday, 1865.

Pondering these revelations, Gates felt a bit disillusioned with his hero. Then his colleague Goodwin — whom he says played Yoda, the sagacious advisor, to his questing Luke Skywalker — snapped him out of it. “Get over it,” she told him. “It’s not his fault. It’s the fault of all the historians who’ve represented him this way.”

Gates began to reconsider Lincoln in this new light, recalling W.E.B. DuBois‘ adage that Lincoln was “big enough to be inconsistent.” “It was like a boil being lanced,” he says of being freed from the burden of his idealized views of Lincoln. “It was a relief.”

Gates says that the idealization of Lincoln served different agendas for white and black Americans. The myth of Lincoln the Saint salved white consciences by allowing America’s Anglo-European majority to tell itself that it had done its part to liberate blacks by fighting the Civil War, and any further social progress was up to African Americans themselves.

The same myth may have impeded blacks by creating a shining model of white behavior that bore scant resemblance to the attitudes of most white Americans from the 1870s through at least the 1930s, a period that Gates calls “the nadir of black-white relations.”

For the historian, researching the program “challenged me to be tolerant of diverse views at the extremes,” never more so than when he attended a convocation of the Sons of Confederate Veterans. On camera, Gates assiduously avoids making judgments about the perspective of the organization or its members. “It’s easy to be a professor at an Ivy League school where everybody’s a liberal,” he says. “But I had to put myself inside the heads” of SCV members.

If there’s a moral to the epic, multi-shaded story of Lincoln’s evolving racial attitudes, Gates believes it’s that his example demonstrates how any of us likewise can modify or put aside our prejudices.

“Race and racism haven’t gone anywhere. But I think the capacity to confront one’s limitations, stare them in the eyes and become a better person in the larger good is what I want people to take away from the film.”