Mengering died Tuesday, Letterman's rep told The Associated Press. Her death came one day before Letterman's 70th birthday.
Known as "Dave's Mom," Mengering, who was a church secretary, typically appeared via satellite from her Carmel, Ind., home around Mother's Day and Thanksgiving for her son's "Guess Mom's Pies" segment.
"After Lillehammer, I couldn't believe how it all took off," Mengering told The New York Times in 1996. "I think it's about the idea of mom and of a family. People are eager for families to be like they used to be. Even though there are lots of working moms and single-parent families now, you can still be a family in spite of the size and form it takes."
She subsequently "covered" the next two Winter Olympics in Nagano and Salt Lake City.
In 1996, Mengering published a cookbook, Home Cookin' With Dave's Mom, which contained recipes for her famous pies and several favorite dishes of her children ("Dave's Fried Baloney Sandwich," "Jan's Sauerkraut Balls" and "Gretchen's Salad Dressing").
An Indiana native, Mengering married Letterman's father, Harry Letterman, a florist, in 1942. After Harry's death from a heart attack in 1973, she married Hans P. Mengering, a structural engineer, who died in 2013.
Letterman's Late Show successor Stephen Colbert paid tribute to Mengering on Twitter.