When the aspiring poet Horace Traubel met an aging Walt Whitman in 1873, the two developed a special relationship. The younger man visited the older one at his home in Camden, N.J., every day to listen to his mentor’s musings, much to Whitman’s delight.

“You will be called upon many a time in the future to bear witness — to quote these days, our work together, the talks, anxieties — the victories the defeats,” Whitman told Traubel in 1888. “Whatever we do, we must let our history tell the truth.”