As he watched Black citizens declare war on segregation during the bus boycott in Montgomery, Ala., Martin Luther King Jr. realized "there is nothing more majestic than the determined courage of individuals willing to suffer and sacrifice for their freedom and dignity."

More than 50 years after King was murdered, Jonathan Eig (author of "Ali") illustrates how King exemplifies that courage and remains an icon of the civil rights movement. But in hallowing him as a prophet of racial integration and nonviolence, Eig argues, "we have hollowed him." Drawing on recently released FBI files, telephone recordings and interviews for this first full-scale biography in decades, Eig acknowledges King's frailties and failures, as well as his radical critique of economic inequality and the war in Vietnam.

Eig enriches his familiar narrative of King's activism with moving stories of how "his presence radiated through the crowd."

Listening to King, we learn, Francine Yeager — a teenager from Chicago who arrived in Washington, D.C., with a toothbrush, two bottles of Pepsi and one change of underwear in her backpack — suddenly remembered being asked by an elementary school classmate, "Are you white or are you [epithet]?" Having never heard the term, Francine decided she didn't like it, replied "I'm colored," and never played with Geraldine again. After the March on Washington, Walter Stovall, a white man, decided to wear his wedding ring all the time and tell colleagues he was married to Charlayne Hunter, a Black woman.

Eig also details King's character defects. The biographer reminds us that King plagiarized, usually from prominent ministers. Although he knew the FBI was tapping the phones of friends and colleagues, intending to undermine the civil rights movement, King maintained sexual relationships with many women.

Although King appeared to accept the possibility of assassination with equanimity, Eig reveals he feared confrontation, was guilt-ridden, overwhelmed with a sense of responsibility and subject to severe depression, for which he was often hospitalized.

At the end of his life, as race riots erupted throughout the country, King had changed, according to Eig. Although he continued to oppose Black separatism, he had concluded racism was pervasive in the north as well as the south. King now advocated radical reconstruction , including massive urban revitalization and a guaranteed income.

Although almost a thousand cities have streets named in his honor, Eig concludes the only way King can help Americans decide where we go from here is to take seriously his advice that the nation's survival depends on our ability "to adjust to new ideas, to remain vigilant and to face the challenge of change."

Glenn C. Altschuler is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.

King: A Life
By: Jonathan Eig.
Publisher: Farrar, Straus, and Giroux. 688 pp. $35.