* Greg Heffley: The protagonist and narrator of the story. He is a middle school student who is trying to navigate the challenges of summer vacation.
* Rodrick Heffley: Greg's older brother, who is a high school student and often makes Greg's life miserable.
* Manny Heffley: Greg's younger brother, who is a toddler and often gets into trouble.
* Susan Heffley: Greg's mother, who is trying to keep the family entertained and organized during the summer.
* Frank Heffley: Greg's father, who is often working and doesn't always understand what Greg is going through.
* Rowley Jefferson: Greg's best friend, who is also trying to figure out how to have a good summer.
* Chirag Gupta: Rowley's friend who is a bit more mature than Greg and Rowley, but still willing to join in their adventures.
The book also features a number of other supporting characters, including Greg's classmates, teachers, and neighbors.