Biography often is the art of reconciling opposites. Robert Caro, the prize-winning biographer of New York municipal builder Robert Moses and Lyndon Johnson, has taken on men who have both inspired and dismayed him. A former investigative journalist, Caro sees his job as collecting as much information as possible and only then forming opinions. There is no such thing as “objective truth,” he says, but there are enough “objective facts” to bring you close.

For his Moses and Johnson books, Caro has relied upon countless documents and interviews. He has labeled his Johnson series, begun soon after the president’s death and still going, as a narrative of darkness and light, of the basest cruelty and the noblest achievement. His Moses book, The Power Broker, was another epic of greatness and destruction and even more complicated to write because he interviewed Moses.

“You were awed by seeing the scope of his vision as he talked about it to you and explained it to you. You see him standing in front of this map, with a yellow pencil and sharp point, just gesturing toward this tri-state area that he sees as one entity and has a vision for it,” says Caro, whose book was harshly criticized by Moses, but won the Pulitzer in 1975 and is now standard reading.

“But I was simultaneously talking to the people he had displaced, hounded them out of their homes. You have to show both of these things, his genius and its effect on people.”

Authors have followed paths they never imagined before starting a book or encountering the subject. Edmund Morris was a prize-winning biographer of Theodore Roosevelt, but the chance to write about a living president led him to take unusual license. Granted years of access to Ronald Reagan, Morris was left so mystified that he inserted a fictionalized version of himself into the book, Dutch, as a way of making sense out of the president.

Jane Leavy, author of a well-regarded biography on Mickey Mantle, said she had a hard time starting the book because of her childhood worship for the New York Yankees star. She decided the best way to move ahead was to acknowledge up front her memories, and map out the life of the flawed and troubled man she came to know and to hear about.

“He was multidimensional and far more complicated than the hagiographic biographies I read in school or the dark stories about him being a womanizer and an offensive drunk,” she says. “No one is one way or another. The fact he was horrible to his wife doesn’t invalidate his skill. So the task became why he treated people the way he did. And that’s the biographer’s job.”