 The Mellotron became a key instrument in progressive rock . King Crimson bought two Mellotrons when forming in 1969 . They were aware of Pinder 's contributions to the Moody Blues and didn 't want to sound similar , but concluded there was no other way of generating the orchestral sound . The instrument was originally played by Ian McDonald , and subsequently by Robert Fripp on McDonald 's departure . Later member David Cross recalled he didn 't particularly want to play the Mellotron , but felt that it was simply what he needed to do as a member of the band . Tony Banks bought a Mellotron from Fripp in 1971 , which he claimed was previously used by King Crimson , to use with Genesis . He decided to approach the instrument in a different way to a typical orchestra , using block chords , and later stated that he used it in the same manner as a synth pad on later albums . His unaccompanied introduction to " Watcher of the Skies " on the album Foxtrot ( 1972 ) , played on a Mk II with combined strings and brass , became significant enough that Streetly Electronics provided a " Watcher Mix " sound with the M4000 . Banks claims to still have a Mellotron in storage , but doesn 't feel inclined to use it as he generally prefers to use up @-@ to @-@ date technology . Barclay James Harvest 's Woolly Wolstenholme bought an M300 primarily to use for string sounds , and continued to play the instrument live into the 2000s as part of a reformed band . 
