Blair Cornelia Waldorf is the main character of the Gossip Girl book series, also appearing in the television adaptation of the same name. In addition to being the protagonist of the original novels, she is the most widely publicized figure from the television series, and the most critically acclaimed character of both. Blair was initially introduced as a supporting character to the intended lead, Serena, but took increasingly over the series as author and reader alike responded to her more. Additionally, she is the creation who author Cecily von Ziegesar has labeled as her most complex.

The television character, played by Leighton Meester, has gained a high degree of notability for her popular wardrobe. As a result, her styles and outfits have received real-life coverage or recognition from various periodicals.

A privileged young woman born to high society, Blair is presented as the beautiful Queen Bee of Manhattan's social scene. Due to her status on the Upper East Side, Blair's actions and relations are under constant scrutiny from the mysterious Gossip Girl, a popular blogger.

Both the author and television actress have openly commented on the character's motivations. According to Meester, some of Blair's biggest vices are her "insecurities" with regard to her social status, which often make her an overachiever. This is partly due to a certain degree of jealousy she feels toward her friend and occasional rival, Serena. At times, these insecurities create what von Ziegesar labels "flaws and complexities" which contribute to character development. In Meester's view, the true Blair is a "good girl" who possesses a more sensitive and good-natured center.