The influential American historian born in 1955 known for their research on social movements and political theory is Howard Zinn. Zinn is best recognized for his book "A People's History of the United States," which presents history from the perspective of marginalized groups, challenging traditional narratives. His work emphasizes the importance of activism and collective action in shaping history, and he advocates for social justice and equality. Zinn's unique approach has had a lasting impact on historical scholarship and the way history is taught in schools, encouraging critical thinking and inclusivity in historical discourse.