Dorothy Mengering
Dorothy Marie Mengering ( née Hofert , formerly Letterman; July 18 , 1921 – April 11 , 2017 ) , better known to "Late Night" and "Late Show" viewers as Dave's Mom , was the mother of late-night talk show host David Letterman and frequent telephone and live guest on his show . 
<triplet> Late Night <subj> David Letterman <obj> cast member <triplet> Late Show <subj> David Letterman <obj> presenter