The famous lawyer known for advocacy on behalf of the underprivileged is Thurgood Marshall. As a key figure in the civil rights movement, Marshall served as the chief legal counsel for the NAACP and played a crucial role in the landmark case Brown v. Board of Education, which declared racial segregation in public schools unconstitutional. His steadfast commitment to justice and equality led him to become the first African American Supreme Court Justice, championing civil rights through his judicial career.