Loved this comparison

As Zinoman puts it, “His smirking tone was so consistently knowing that he seemed as if he must know something.”  This was an attitude fit for the cynical mood of the 1980s, and Zinoman emphasizes Letterman’s significance as an avatar of cool noncommitment, a figure of his time.  In that, Letterman resembled that other pop-cultural phenomenon of the era, Jim Davis’s Garfield – the rotund cartoon feline also riven by self-doubt and haunted by grandiose fantasies of domination while projecting an aloofness that often verged on the cruel.

from Naomi Fry’s review of Jason Zinoman’s Letterman: The Last Giant of Late Night in the Summer 2017 issue of BookForum.  (A little behind on my Bookforum).