"The Unforgiven" is one of the slower songs on the self-titled album, Metallica (also known as the Black Album). It also has a sequel, in the form of "The Unforgiven II", from the album ReLoad. (...)
The drum & horn intro was essentially taken from an un-identified Western movie and then reversed so its source would be hidden, as Hetfield later explained on "Classic Albums: Metallica - The Black Album". The band has never disclosed what movie the sound was taken from, although it is strongly reminiscent of a segment of Ennio Morricone's "The showdown" from the movie "For a few dollars more".
"The Unforgiven" was played live as part of Metallica's Nowhere Else To Roam world tour which lasted from 1991-1993, in support of the Black Album. It was played again on the Madly in Anger with the World world tour in 2003-2004 and the Escape from the Studio '06 tour. It has most recently been played as part of the 'Sick of the Studio' tour.