It mightn't seem obvious now, but Michael Keaton really started out as a stand up comic, and was actually doing it before David Letterman.
As Letterman's show winds down, every star is going on and telling the legendary host how much they'll miss him. And to be fair, Letterman is the greatest. But Keaton and Letterman know each other a very long time, and there's a genuine affection between the two guys.
Here's Keaton on promoting Batman in the 80s, answering who'd win in a fight - Batman or Mike Tyson.