‘This is Spinal Tap’ Rob Reiner’s 1984 mockumentary about a middle-aged heavy metal band desperately trying to stay relevant is so crammed with gags — visual and spoken — that you can watch it repeatedly and still not catch them all. Even more impressive is the fact that those gags were mostly improvised by Reiner (playing filmmaker Marty Di Bergi) and the rest of the cast, including the band members — frontman David St. Hubbins (Michael McKean), lead guitarist Nigel Tufnell (Christopher Guest) and bassist Derek Smalls (Harry Shearer).