This is Spinal Tap was supposed to be a satirical peek into the decadent, self-contained world of early Eighties heavy metal -- at least as it applied to a group of aging rock stars. At some point, though, the movie transitioned from cult comedy to cultural institution (In 2002, the Library of Congress selected This Is Spinal Tap for preservation in the United States National Film Registry as a "culturally, historically or aesthetically significant" film).