This Is Spinal Tap (stylized as This Is Spın̈al Tap: A Rockumentary by Martin Di Bergi) is a 1984 American mockumentary film directed and co-written by Rob Reiner. It stars Christopher Guest, Michael McKean, and Harry Shearer as members of the fictional English heavy metal band Spinal Tap (who are characterized as "one of England's loudest bands"), and Reiner as Martin "Marty" Di Bergi, a documentary filmmaker who follows them on their American tour. The film satirizes the behavior and musical pretensions of rock bands and the hagiographic tendencies of rock documentaries such as Gimme Shelter (1970), The Song Remains the Same (1976), and The Last Waltz (1978). Most of its dialogue was improvised and dozens of hours were filmed.

References:
https://en.wikipedia.org/wiki/This_Is_Spinal_Tap