The famous figure known for his letters from Birmingham Jail is Martin Luther King Jr.. In these letters, written while he was imprisoned for participating in nonviolent protests against racial segregation, King articulated his philosophy of nonviolence and the necessity of direct action to combat injustice. He addressed criticisms from white clergy and emphasized the urgency of civil rights, laying out the moral imperative for dismantling systemic racism. King's writings continue to serve as a foundational text in the civil rights movement and a call to action for contemporary social justice advocates.