Frank Heffley

Frank Heffley is Greg's, Rodrick's, and Manny's unpredictable and always-serious father. He is the husband of Susan Heffley (Greg's mom) and the Brother of Uncle Joe.

Personality
Frank is unpredictable, serious and emotional. Frank has a strong interest in American History, and this is implied in Rodrick Rules, as he builds up a Civil War Battlefield in his spare time. So far, he is exceedingly very emotional to Greg. He is constantly bothered and troubled by such small matters, such as Rodrick's typing skills and Greg's silly mistakes, and always wants his sons to look good in his boss, a very small matter that Frank constantly gets worked up about. Frank hates video games, his younger brother, heavy metal music, Rowley and more respectively, teenage delinquents. He is a hard worker, and has a poor relationship with all of his sons, since the three cannot relate to each other at all in any way possible.

Greg Heffley
Greg and Frank, overall have a poor relationship. In Diary of a Wimpy Kid: The Last Straw, Frank gets fed up with Greg's behavior and threatens to send his son to Spag Union Military Academy to toughen him up, because the academy turned Lenwood Heath, a prankster, into a polite young man. Greg tries to circumvent this by proving to his dad that he does not deserve this treatment by "doing his best" in soccer and joining the Boy Scouts, among other things, but ultimately fails. It is not until Seth Snella's half-birthday party that Frank realizes that his son's wimpiness is a good thing, because it saved himself from looking foolish in front of the entire town. It is in Dog Days, where their relationship completely break down.

Grandpa Heffley
Frank and Grandpa have a tense relationship, as shown in Dog Days. Frank has a rather minor role in the story until Father's Day, where Grandpa admits that he lied to him about his dog, Nutty, running off to a "butterfly farm", and instead admitted that he accidentally killed his dog. Frank, in response, becomes furious, and decides to buy another dog to make up for the lost one. This dog was named "Sweetheart" much to the three siblings' dismay, or Sweetie for short. Frank becomes obsessed with this dog, even though Sweetie is two times as lazy and repulsive as Greg.

Trivia

 * Frank's actual profession is not listed so far. Greg, however does know what his father does for a living. Apparently, It may be hinted that Greg has no intention of telling what he knows.