The confidant feminine: confidante, same pronunciation) is a character in a story that the lead character (protagonist) confides in and trusts. Typically, these consist of the best friend, relative, doctor or boss.
The confidant provides the writer of the story with a plausible device for communicating to the audience the mind and intention of their principal character (protagonist). The protagonist may reveal their secrets, personal problems and character flaws to the audience through their conversations and interactions with the confidant character, often entrusting them with important information about themselves (as well as information critical to the plot) that they would not entrust to other characters. The type of character used as a confidant is most commonly the protagonist's closest friend, but may also be a family member such as a spouse, sibling or parental figure, co-worker, trainer or a health professional such as their psychiatrist.
Confidants may not only be used for conveying information about the plot to the audience, but may also be used to share information about the protagonist (such as their feelings about certain subjects or personal fears). In this way, the audience can get to know the protagonist and their goals, as well as their personality and role in the story. Therefore, the confidant is likely to be the only character in the story to know the protagonist's secrets or hidden agendas (and even if they are not the only ones to know, they would at least be the very first ones to know other than the protagonist themselves).