|Film Appearance?||Yes (Bonus feature only)|
Gammie Heffley is Greg, Rodrick, and Manny's extremely elderly paternal great-grandmother of around 95. She is the grandmother of Frank, Joe and Gary Heffley and the mother of Grandpa. She is the oldest living member of the Heffley family and the widow of Greg's late great-grandpa Chester. Gammie has only appeared in The Ugly Truth, but had a major role in the story.
Gammie has a lot of wisdom and traditionally gives "The Talk" to her older grandchildren and great-grandchildren on the edge of becoming teenagers. Gammie likes visitors as she often makes meals for them. Her furniture is also very valuable, and people often leave notes with their names on her possessions, so they can claim it when Gammie dies. Her last appearance in the book is when she gives "The Talk" to Greg about how he shouldn't be too excited about growing up, but Greg leaves after she pulls up her leg to show Greg medical conditions older people can get. In Cabin Fever, it was mentioned that she gave Susan Heffley a spoon carousel.
- Diary of a Wimpy Kid: The Ugly Truth (First appearance)
- Diary of a Wimpy Kid: Cabin Fever (Mentioned)
- Diary of a Wimpy Kid: Class Clown
- Happy Meal Commercial
- The Wimpy Kid: Do it Yourself Book
- Gammie is one of the few characters in the series to have a confirmed age of 95. She would, therefore, be born around 1916.
- According to the family tree in "The Wimpy Kid Do-It-Yourself Book", Gammie is on Susan's side of the family (as Grampa's mother). However, when she later appeared in "The Ugly Truth", she was said to be on Frank's side instead, meaning she is either Grandpa or Nana's mother
- In a flashback in Diary of a Wimpy Kid: Cabin Fever, when Greg sneaks into his mother's, email account to tell everyone to coordinate all of the Christmas presents he will get, Gammie's name can be seen on the computer.
- Gammie made an appearance in a McDonald's Happy Meal Commercial alongside The Pig, Rodrick, and Sweetie.