- "Murp Rrup"
- —The 2 most common lines of Arthur Heffley.
Arthur Heffley is the great-uncle of Greg Heffley. He doesn't say words and instead says weird sounds like "Murp" and "Rrup". He only appeared briefly in "The Ugly Truth", when the family stayed at Gammie's house for Uncle Gary's wedding. He is replaced by Clyde Heffley in the online version. Greg tends to not take what he is offering in Diary of a Wimpy Kid: The Ugly Truth at dinner
- The possible reason why he can not talk may be due to a mental illness.
- He is Grandpa's brother, being born around 1942.
- Byron Heffley is probably his son.