*Holly Elizabeth Hills (known as Piper Elizabeth Matthews in the online book) is the younger sister of Heather Hills who serves as a major love interest for Greg Heffley in the early books and in the live action film adaptations. Holly Hills is the most popular girl in Greg's grade, but she is considered to be the fourth prettiest girl in their grade, however, the top three prettiest girls are mentioned to all have boyfriends. It is implied that Holly and Greg became a couple in the film adaptation of Dog Days.

However, her character undergoes more extensive development in the movies. There, she emerges as a multidimensional personality, unveiling various aspects of her life.

In the film adaptations, Holly's character is enriched as she is portrayed as a member of a girls' soccer team, a professional model, and a former class president during her sixth-grade year, as disclosed by Chirag Gupta. This makes her athletic and she doesn't mind getting her pictures taken. With a girl-next-door attitude, she exudes a sweet and caring nature, emanating a heart of gold. She is down-to-earth as well.

Furthermore, these adaptations reveal that Holly has an older sister with a somewhat unpleasant disposition and a younger sister who is somewhat spoiled, drawing parallels to Greg's experiences with his own brothers. This shared experience becomes a point of connection and bonding between Holly and Greg.

In the climactic scene of the third film, an intriguing development unfolds as Holly holds Greg's hand after the resolution of an incident involving Heather. This gesture hints at a potential mutual attraction between the two characters, suggesting that Holly might harbor feelings for Greg as well.

Through the additional depth given to Holly's character in the movies, the audience gains a deeper appreciation for her personality and her role in the story-line, adding a layer of complexity to the overall narrative. It was revealed that she was the only four-year-old in preschool who wasn't potty-trained, as told by Susan, as shown in The Last Straw when Greg and Rowley were going to the Roll-A-Round roller rink in Susan's car. She also hasn't appeared since Hard Luck and didn't appear in the Long-Haul film adaptation.

Holly's appearance is thought to be overly attractive, the way Greg depicts her. She is colored black and white, like everybody else in the book. Her notable features include a round, largely sized diamond earring, an ear with an arrow depicted as the insides, she has light colored hair that sits nicely on her shoulders and a skirt that covers her knees. In the movie, she has long, wavy golden-blonde hair, creamy pale skin, hazel-green eyes and is taller than Greg. She has done professional modeling, therefore she knows how to show herself off.*