The significant historical figure behind the "March on Washington" in 1963 was Dr. Martin Luther King Jr. This massive civil rights demonstration aimed to highlight the economic and social injustices faced by African Americans. It gathered over 250,000 participants on August 28, 1963, and became famous for King's iconic "I Have a Dream" speech, which called for racial equality and justice. The march was pivotal in raising awareness and influencing public opinion, ultimately contributing to the passage of landmark legislation like the Civil Rights Act of 1964.