The Square is a respectable mathematician and member of Flatland's professional class. As the narrator, he possesses a deep intellectual curiosity but initially remains bound by the rigid social structures of his two-dimensional world. He values order and geometry, frequently tutoring his grandson and debating with others about the nature of existence.

The Sphere is a three-dimensional being from Spaceland who serves as a guide to higher dimensions. Possessing a physical perfection that stuns Flatlanders, he appears as a flawlessly shifting circle. He is patient but becomes quickly frustrated when his teachings face resistance from those trapped in lower-dimensional thinking.

The Square's Wife is a straight line, as are all women in Flatland. She is fiercely protective of her household and shares a peaceful domestic life with her husband. Though restricted by oppressive gender laws, she displays strong common sense and practicality when managing her home.

The King of Lineland is the monarch of a one-dimensional world. Pompous and self-centered, he is entirely convinced that his straight line constitutes the entirety of space. He vehemently rejects any evidence that challenges his limited perspective.

Chromatistes is a legendary Pentagon from Flatland's history who accidentally discovered the art of painting. By painting his house and family, he inadvertently sparked the Colour Revolt, a massive working-class uprising aimed at erasing social and political distinctions.

The Square's Grandson is a brilliant, unusually promising young Hexagon. His keen intellect leads him to deduce the mathematical possibility of a third dimension, a concept that immediately unnerves his traditional grandfather.

The Square's Brother is a perfectly symmetrical square who holds a high-ranking position within the Flatland government. He executes laws that suppress dangerous knowledge on behalf of the ruling Circles.

Pantocyclus is an illustrious Chief Circle and President of the High Council. He is a cunning and ruthless leader who preserves the dominance of the priestly class by enforcing strict social divides and eliminating threats to the established order.

The Point is an inhabitant of Pointland, the lowest level of existence. He represents an extreme of ignorance and complacency, consisting solely of himself and referring to himself in the third person.

The Square's Sons are four members of the professional class who live with their parents. They represent the continuing generational advancement of Flatland's society and occupy a quiet background role in the family home.