Muscle Princess (also called Princess Muscles) makes her first appearance in "What is Life?" in the circle of princesses Ice King shows Neptr in his imagination zone. She makes a second appearance in "Loyalty to the King" when she is seen in the crowd wanting to marry "Nice King." She makes her third appearance in "To Cut a Woman's Hair" when Finn tries to get a lock of her hair, but she quickly misunderstands him and wants him to get "more serious about loving her." In her appearance in "Princess Monster Wife," she is seen with another group of princesses, complaining that Ice King stole her left arm to make his "Princess Monster Wife." She lives in a castle in the forest. Ice King kidnaps her at the end of the episode "Betty," but she breaks free from her icy restraints and proceeds to pummel him mercilessly. According to "Princess Day" she is considered to be a registered princess. She also tells Peanut Princess that her body needs juice in the episode "Princess Day," revealing a possible reason for her muscular figure.
As her name states, she is a very muscular princess. She is very large and tall, green skinned, and wears dark-blue boots decorated with some type of symbol. Originally, the boots had yellow stars. Afterwards, the boots have light-blue hearts, but in "Princess Monster Wife," the hearts are yellow. She has a small yellow crown on her head. She usually carries a dumbbell and works out her arms. In the episode "To Cut a Woman's Hair" it is revealed she has a deep masculine voice. Her hair is short with two heart-shaped buns on each side of her head; she claims she doesn't make her hair beautiful so people will notice her muscles instead. Her crown, skirt, hairstyle, boots, and lips were redesigned after her cameo in "What is Life?" and she no longer has visible veins, which were part of her original design.
In the episode "Princess Monster Wife," the hearts on Muscle Princess's boots were changed from light blue to yellow and the heart on her crown changed from gold to red. The blue skirt was also lightened to a lighter blue.
She resembles Starla from Regular Show, as both are green-skinned, have two pigtails and are muscular.
In the episode "To Cut a Woman's Hair," Finn called her "Princess Muscles" so she probably can be formally known as both "Muscle Princess" and "Princess Muscles."
According to CN Latin America, her ideal prince has muscles and she plays the drums to pass the time.