Monika (モニカ - meaning "advisor" or "counselor") is the poster girl and primary antagonist of Doki Doki Literature Club!. She is one of the main characters and the president of the Literature Club until she was replaced by Sayori after being deleted in Act 3. Over the course of the game, it is revealed that Monika is self-aware, causing her to create many game-breaking glitches in pursuit of the player. You cannot write poems for her until near the end of the game in Act 3.

Monika has long coral brown hair that she keeps in a ponytail tied back with a large white bow. She also has bangs and two long strands of hair next to her face. Her eyes are emerald green; Act 3 shows tiny dots in what is supposed to be her colored pupils already surrounding the iris.

She wears the typical school uniform, which is a warm gray blazer of a white-collared shirt with a brown sweater vest over it, topped off with a red ribbon. She also wears a dark-blue skirt, black thigh-high socks, and white uwabaki slippers with a pink tip, which are in stark contrast to the rest of the cast's white knee-socks and blue-tipped slippers. She is the second tallest behind Yuri.

Monika is noted by the other characters to be smart, beautiful, confident and athletic. She's not as talkative as the other girls, but this is implied to not be through choice.

Monika had previously been a part of the Debate Club but left due to all the inner politics and drama, highlighting a desire for order, freedom of topics and friendliness. The Literature Club, which she founded after leaving the Debate Club, is very important to her. She aspires for it to be a place to showcase and grow everyone's passion for literature. Monika openly displays care and concern for her club mates, praising each member's writing style and even comparing them to famous authors and poets.

Starting from Act 2, she shows a much more manipulative personality. It is revealed that Monika was self-aware all along and resented from being made into a minor role. She becomes infatuated with the player and urges them to spend more time with her. Monika begins trying to dispose of her club mates so the player is forced to choose her, after her attempts to make the other girls unlikable fail. Her desire and ambition lead her to become obsessive in this goal, highlighted by the fact that all of her poems are about the player or her epiphany.

Despite Monika's upbeat attitude in the Literature Club, it becomes increasingly obvious that she's really sad and lonely, as a result of being aware that her whole world is just a simulation; a simulation in which she can't even achieve what is considered "happiness" (i.e. having her route completed). She fixates on the player so much because they're the only "real" thing in her life. It also doesn't help that, whenever someone quits the game, Monika is trapped in a hellish void of noise, lights, colors, and screams and despite not even being able to form coherent thoughts, she remembers all of it whenever the player turns on the game again.

Later in the game, the player will be able to read Monika's Talk where she talks directly to the player, instead of the protagonist. It is at this point that the player is able to learn much more about Monika's personality, as the player does not have the chance to interact with Monika beyond essentially superficial dialogue until Act 3.