Nikki J. Maxwell - The main character of the series and a new student at Westchester Country Day. Because Nikki feels completely out of place among all the wealthy, designer clad students, she spends most of her time alone writing in her diary. She is 14 years old. Her best friends are Chloe and Zoey (the bestest friend ever)
MacKenzie Hollister - The most popular girl at Westchester Country Day and the leader of the CCP (Cute, Cool & Popular) clique. MacKenzie hates Nikki's guts and makes fun of her. She talks behind Nikki's back and tries to wreck her life with the help of her best friend, Jessica Hunter.
Brandon Roberts - Nikki and MacKenzie's crush. He is not as impressed by MacKenzie as everybody else - it is obvious that he has feelings for Nikki more. He is charming, polite, handsome and a dork. His grandmother owns a pet adoption group, Fuzzy Friends.
Chloe Garcia - One of Nikki’s best friends. Chloe is an avid reader and loves young adult romances. She is a self-proclaimed expert on guys and dating. She is the 5th most unpopular girl at Westchester Country Day. She is Hispanic and has long blonde hair with bangs.
Zoey Franklin - One of Nikki’s best friends. Intelligent and also an avid reader, she loves self-help books and is a self-proclaimed expert in psychology. Nikki describes her as a "human Wikipedia." Zoey is the 7th most unpopular girl in the school. She is African-American and has medium length hair and bangs.Brianna Maxwell - Nikki’s bratty little 6-year-old sister. She has a friend named Miss Penelope (which is her own hand with a face drawn on it with an ink pen). Brianna attends ballet classes and constantly gets into trouble by doing things such as sneaking cookies out of the cookie jar or drawing pictures on the walls only to blame it on Miss Penelope.
Jessica Hunter - The second highest-ranking CCP at WCD and MacKenzie's best friend. Just as MacKenzie, she does not like Nikki and is extremely rude to her.
Violet Baker - The most popular person out of the unpopular. She is shown to be handicapped in a wheelchair, but the reason for this is unknown. She is one of the members of Nikki's band, Actually, I'm Not Really Sure Yet.
Theodore L. Swagmire III - One of the unpopular boys in WCD and one of Nikki's friends. He became friends with Nikki in the second book by helping out with the Halloween dance. He had a big crush on Mackenzie and now likes Zoey. He is one the members of Nikki's band.
Marcy Simms - Nikki meets Marcy through her post as Miss-Know-It-All. Marcy sends an anonymous letter to Miss Know-It-All, saying that she's new, being bullied by some other girls, and can't find friends. Nikki tells her to hang in there, and keeps a look out for the new girl. She soon finds it's Marcy, and invites her to Brandon's birthday party, where Marcy has a great time. Marcy is MacKenzie's assistant fashion director for the newspaper, but is bullied by MacKenzie, and is deemed to be unfashionable by the latter.