4. Dave's Mom
If you're looking for the single most beloved Late Night/Late Show supporting player, stop here. With her petite frame, happy smile and big glasses, white-haired Dorothy Mengering (a.k.a. Dave's Mom) was the perfect embodiment of a mother: She clearly loves her son while politely tolerating his foolishness with the sort of doting affection only a parent understands. In a world where everybody refers to Letterman by the more familiar "Dave," Dorothy was the one person who called him "David," and it was sweet enough to melt your heart. Whether she was covering the Winter Games or simply checking in from her Indianapolis home every Thanksgiving, she conveyed an unassuming Midwestern earnestness that was endlessly disarming. Amidst the show's witty, edgy spirit, she provided the heart.