2. Chris Elliott
Chris Elliott will always be most associated with Dave's show for his 1989 appearance where he tested two kinds of dog food — "I can't tell too much difference between the two," he nonchalantly reported — but the performer was a Swiss Army Knife of comedy, able to do just about anything. He'd come on Late Night as a guest but then pretend he was, say, Jay Leno, Marv Albert or Marlon Brando (the latter doing his "famous" banana dance). There was a terrific recurring segment called "Guy Under the Seats," in which it was established that Elliott lived beneath the audience bleachers, occasionally popping up to unleash some random madness. Mostly, though, the comedian provided Letterman's first late-night show with a consistent blast of irreverence laced with just enough anger and bite to leave you wary. During his final Late Show appearance, the host called him the "funniest man I've ever worked with." It's also possible he's the show's most underrated comic force.