Cady Heron is a 16-year-old junior with long auburn hair, blue eyes, fair skin, and a tall, slim build. Raised in Africa by zoologist parents and homeschooled before moving to Illinois, she is curious, strong in math, and initially unfamiliar with high-school cliques. Wanting to fit in draws her into the Plastics’ games and strains her friendship with Janis and Damian. Earnest and observant, Cady can admit when she has caused harm; Mathletes and Spring Fling help her reclaim her identity.

Regina is a 16-year-old junior with long blonde hair, blue eyes, fair skin, and a polished, slender appearance. As the Plastics’ leader, she is confident, socially perceptive, stylish, and skilled at controlling the school’s pecking order. She can be cutting and manipulative, especially when challenged, yet her confidence is shaken when Cady gains popularity and Aaron becomes involved. After the Spring Fling, Regina begins channeling her energy into lacrosse.

Gretchen is a 16-year-old junior with long chestnut-brown hair, brown eyes, fair skin, and a neat, preppy style. Regina’s closest follower among the Plastics, she is observant, talkative, and eager to be included. Her loyalty can turn into gossip when Regina expects it. Cady’s rise exposes Gretchen’s insecurity, but she gradually starts speaking up and building friendships on her own terms.

Karen is a 16-year-old junior with long blonde hair, blue eyes, fair skin, and a carefully coordinated, feminine style. She is cheerful, affectionate, literal-minded, and more perceptive than people assume. As one of the Plastics, she follows Regina’s lead but also shows warmth toward Cady. Karen’s openness and humor help her keep her own sense of self amid the school’s status games.

Janis is a 16-year-old junior with dark shoulder-length hair, dark eyes, fair skin, and an alternative, artful style. Wry, creative, independent, and fiercely loyal to Damian, she knows North Shore’s social landscape well. Her former friendship with Regina ended bitterly, and she recruits Cady to expose Regina’s behavior; her anger sometimes pushes the plan too far.

Damian is a 16-year-old junior with dark, slightly curly hair, brown eyes, fair skin, and an expressive, colorful style. Funny, welcoming, quick-witted, and socially confident, he is Janis’s closest friend and helps Cady navigate North Shore. Damian notices how cliques work but values genuine friendship more than status, and he is hurt when Cady’s new popularity pulls her away.

Aaron is a 17-year-old junior with short brown hair, brown eyes, fair skin, and a tall, athletic build. Friendly and relaxed, he is Regina’s former boyfriend and Cady’s crush. He wants to make his own choices rather than be managed by Regina’s social games. His interest in Cady intensifies the rivalry between the girls and pushes him to set clearer boundaries.

Ms. Norbury is a middle-aged math teacher with shoulder-length dark hair, brown eyes, and a practical, understated style. Patient, perceptive, and dryly funny, she recognizes Cady’s talent and encourages her to join the Mathletes. She tries to guide students through the fallout from the Burn Book while keeping the classroom focused and fair.

Kevin is a 17-year-old senior with short dark hair, brown eyes, medium-brown skin, and a neat school style. Confident, disciplined, and competitive, he captains North Shore’s Mathletes. He recognizes Cady’s talent and gives her a place on the team, where her skills matter more than her popularity.

Mrs. George is Regina’s warm, image-conscious mother, a blonde, fair-skinned woman with bright eyes and an upbeat, youthful style. She wants Regina to feel adored and popular, often trying to be a friend more than a parent. Her open-hearted enthusiasm provides a comic contrast to the tension inside the Plastics and the George household.