MUST SEE: 14 Candid PHOTOS of Martin Luther King, Jr.

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Yesterday was Martin Luther King Day, the federal holiday that celebrates the life of the civil rights activist. The holiday—signed into law by President Ronald Reagan in 1983, and observed since 1986—is held on the third Monday in January. (King was born on January 15.) Here's a look back at King in action.

Photos and captions courtesy of Getty Images.

1. American civil rights leader Dr. Martin Luther King, Jr. sits on a couch and speaks on the telephone after encountering a white mob protesting against the Freedom Riders in Montgomery, Alabama, on May 26, 1961.

2. American civil rights campaigner Martin Luther King arriving at London Airport on October 1, 1961. He was in England to be the chief speaker at a public meeting about color prejudice and to appear on the BBC television programme Face To Face.

3. American president John F. Kennedy in the White House on August 28, 1963, with leaders of the civil rights March on Washington (left to right): Dr. Martin Luther King, Rabbi Joachim Prinz, A. Philip Randolph, President Kennedy, Walter Reuther and Roy Wilkins. Behind Reuther is Vice President Lyndon Johnson.

4. King raising his hands in a restaurant on September 21, 1963.

5. Canon John Collins greeting King at London Airport on December 5, 1964.

6. King receives the Nobel Prize for Peace from Gunnar Jahn, president of the Nobel Prize Committee, in Oslo, on December 10, 1964.

7. President Lyndon B. Johnson discusses the Voting Rights Act with King in January 1965. The act, part of President Johnson's "Great Society" program, trebled the number of black voters in the south, who had previously been hindered by racially inspired laws.

8. King and his wife, Coretta Scott King, lead a civil rights march from Selma, Alabama, to the state capital in Montgomery in March 1965. On the left (holding bottle) is American diplomat Ralph Bunche.

9. King addresses a crowd in front of the Capitol Building in Montgomery, Alabama, following a voting rights march from Selma, Alabama, in March 1965.

10. King listening to a transistor radio in the front line of the third march from Selma to Montgomery, Alabama, to campaign for proper registration of black voters, on March 23, 1965. Among the other marchers are: Ralph Abernathy (1926 - 1990, second from left), Ralph Bunche (1903 - 1971, third from right) and Rabbi Abraham Joshua Heschel (1907 - 1972, far right). The first march ended in violence when marchers were attacked by police. The second was aborted after a legal injunction was issued.

11. King addresses civil rights marchers in Selma, Alabama, in April 1965.

12. King speaks to reporters during a march en route to Jackson, Mississippi, on June 11, 1966.

13. Watched by Dr. Charles Bousenquet, King signs the Degree Roll at Newcastle University after receiving an honorary Doctor of Civil Law degree, Newcastle, England, on November 14, 1967.

14. King speaks at a January 12, 1968 press conference for Clergy & Laymen Concerned About Vietnam, held at the Belmont Plaza Hotel, New York City. He announced the Poor People's March On Washington at this event.