Today David Letterman celebrates his 30th anniversary in late night, and does so with little fanfare: No special, no clip packages, just a visit from one of his favorite guests, Howard Stern. As Late Show executive producer Rob Burnett told the New York Times, "[Dave's] not someone who likes to draw attention to himself.” Fine: So we will. In a time when late night has become increasingly diffuse and Dave often gets lost amid such younger competition as Adult Swim and The Daily Show, it is worth a refresher course on just how revolutionary and brilliant a comedy force he has been. We scoured YouTube to find classic clips that give the fullest (but least repetitive: no Velcro suit!) picture of just why Letterman shaped the senses of humor of just about everyone else under 50 currently doing comedy on television. From forgotten old delights like the Thrill Cam and eating fast food with Zsa Zsa Gabor, to recurring staples such as Chris Elliott's visits and the Late Night concept shows, this slideshow is a wormhole of hilarious gems. You may lose your afternoon, but attention must be paid.