The leader of the American civil rights movement known for his "I Have a Dream" speech was Martin Luther King Jr.. He played a pivotal role in advocating for racial equality and nonviolent resistance during the 1960s. His speech delivered during the March on Washington in 1963 is considered one of the most significant speeches in American history. King emphasized the need for civil rights and justice, calling for an end to racism and the fulfillment of the American dream for all people, regardless of race.