Martin Luther King, Jr. (January 15, 1929 – April 4, 1968) was an American pastor, activist, humanitarian, and leader in the African-American Civil Rights Movement.He is best known for his role in the advancement of civil rights using nonviolent civil disobedience based on his Christian beliefs.artin Luther King, Jr. (January 15, 1929 – April 4, 1968) was an American pastor, activist, humanitarian, and leader in the African-American Civil Rights Movement.