On April 15, 1837, a "long, gawky" Abraham Lincoln walked into Joshua Speed's dry-goods store in Springfield, Illinois, and asked what it would cost to buy the materials for a bed. Speed said seventeen dollars, which Lincoln didn't have. He asked for a loan to cover that amount until Christmas. Speed was taken with his visitor, but, as he said later, "I never saw so gloomy and melancholy a face." Speed suggested Lincoln stay with him in a room over his store for free and share his large double bed. What began would become one of the most important friendships in American history.

Speed...