Byron Heffley is the cousin of Frank, Joe and Gary Heffley. He appeared in The Ugly Truth at Gary's wedding. In one reunion, he and Greg were sent to get some milk,but Byron hit a pole, crashing his car and told Greg to get some help from Gammie's house. Greg went inside the house, but the ladies told him to take off his shoes as they were tracking mud. Greg took off his shoes, sat on the couch and watched TV, but Byron came back angry since Greg didn't come back to help him.
- Diary of a Wimpy Kid: The Ugly Truth (First appearance)
- Diary of a Wimpy Kid: Cabin Fever (Indirectly Mentioned)
- In a flashback in Cabin Fever, when Greg snuck into his mother's email account to tell everyone to coordinate all of the Christmas presents Greg will get, Byron's name can be seen on the computer.