Here is the list of some characters that have appeared in all or some of the ten Dork Diaries books so far, or have been mentioned in her blog.
Nicole 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). She has a frenemy named Mackenzie Hollister, one of the main characters and the most popular girl in school
MacKenzie Hollister - The former most popular girl at Westchester Country Day and the former 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 former best friend, Jessica Hunter. MacKenzie is now currently attending North Hampton Hills International Academy, but transferred back to WCD at the end of 11th book
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 one of the most popular students, but he sees himself as a loner and a dork. His grandmother owns a pet adoption group, Fuzzy Friends. He is also fluent in French
Chloe Christina 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 Latina and has long blonde hair with bangs.
Zoey Ebony 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 black medium length hair and two side bangs
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 highest-ranking CCP at WCD and MacKenzie's former 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 but now likes Zoey. He is one the members of Nikki's band, and is close friends with Brandon.
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.
Max Crumbly-A boy introduced in Dork Diaries: Tales from a Not-So-Perfect Pet Sitter. He helped Nikki and Brandon clean up Holly and her puppies, and later took the blame for them in the school. Nikki says he's "Almost as cute as Brandon", which Chloe agrees on, and he's the only Dork Diaries character to get a side series. He's best friends with Brandon Roberts. And he's fully aware that he's crushing on Nikki. He has a crush on Erin Madison
Patrick Clark- He has only been introduced on the Dork Diaries website, and it is not known if he will ever appear in the series. It is hinted that he has a crush on Nikki Maxwell, the main character, due to he doesn't bully her, and he's quiet when she's around. however, it's not confirmed it that's true, it's just something fans is thinking