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"MLK" is the tenth and final song from U2's 1984 album, The Unforgettable Fire. A lullaby to honor Martin Luther King, Jr., it is a short, pensive piece with simple lyrics. It was because of this song, along with "Pride (In the Name of Love)", another tribute to King, that earned Bono the highest honor of the King Center, an organization founded by Coretta Scott King.
Its live debut was on 18 October 1984, as an intro to "The Unforgettable Fire", and the two songs were performed together at almost all Unforgettable Fire Tour shows and most Joshua Tree Tour shows. However, by the end of the Joshua Tree Tour, the band started to use "MLK" to precede other songs, especially "One Tree Hill", and it continued in this capacity on the Lovetown Tour. It failed to appear on the Zoo TV Tour but returned to the setlist on the PopMart Tour, especially after the deaths of Diana, Princess of Wales and Michael Hutchence. It went into another hiatus after PopMart, missing the entire Elevation Tour, but was notably performed as the intro to "Where the Streets Have No Name" at U2's appearance during the Super Bowl halftime show in 2002. After the death of Rosa Parks, it made five Vertigo Tour appearances; in all five instances, it was sung after "One" to conclude the main set. MLK was a part of the main set list for the U2 360° Tour, as the prelude to the song Walk On (U2 song) and to be hopeful for the release of Aung San Suu Kyi from house arrest.
"MLK" was director Richard Kelly's original choice for the soundtrack to the final sequence of Donnie Darko. After difficulties licensing the song, it was decided to use Gary Jules' rendition of the Tears for Fears song "Mad World" instead.
In the novel The Perks of Being a Wallflower, "MLK" is mentioned as one of the character's favorite songs, along with "Blackbird".