"Knockin' on Heaven's Door" is a song written and performed by Bob Dylan for the soundtrack of the 1973 film Pat Garrett & Billy the Kid. The song reached #12 on the Billboard Hot 100 singles chart. The song consists of four chords in the key of A major 7: G, D, Am7, and C. The basic pattern throughout the song is G-D-Am7-Am7 and then G-D-C-C, and this is repeated. In 2004, it was voted #190 by representatives of the music industry and press in Rolling Stone magazine's 500 Greatest Songs of All Time issue.
Although it was originally recorded as an acoustic folk song, "Knockin' On Heaven's Door" has been covered in many tempos and styles, by many artists, most famously Guns N' Roses (which reached #2 in the UK Singles Chart) and Eric Clapton, also by The Grateful Dead, Bryan Ferry, The Alarm, Mark Knopfler, Wyclef Jean, The Sisters of Mercy, Warren Zevon, Seether, Cold Chisel, U2, Roger Waters, Television, Guided By Voices, Avril Lavigne, Aerosmith, Daniel Lioneye, Off target ...
full article at wikipedia