1. This Is Spinal Tap (1984) – Director

Rob Reiner launched his directing career with this groundbreaking mockumentary about a hapless British heavy metal band. Playing fictional filmmaker Marty DiBergi on-screen, Reiner also directed the film, which pioneered a new comedic format. Its improvised style and razor-sharp satire made it a cult classic, influencing generations of comedians and filmmakers. Few debut films have had such a lasting cultural impact.