On August 28, 1963, a quarter of a million people gathered at the Lincoln Memorial to insist that America honor promises it had written into its founding documents but repeatedly denied to Black citizens. Dr. Martin Luther King Jr. gave that demand its most enduring language. But the day was never only about a dream.

The Fifteenth Amendment, ratified in 1870, had already declared that the right of citizens to vote could not be denied because of race, color or previous condition of servitude. But between a constitutional promise and the lived reality of Black Americans stood nearly a century of organized resistance.

For the Basketball Hall of Famer, an early life of segregation and racism shaped his actions for fairness and equality By Martenzie...