The Sphere is a three-dimensional being who introduces the Square to the concept of Spaceland. He possesses a graceful and perfect form that stuns the Square, and he serves as a guide to new dimensions.

The Square’s Wife is a character portrayed within the context of Flatland's social norms, where women are devalued. She shares a loving though constrained relationship with the Square and is protective of their home.

The King of Lineland is a ruler the Square encounters in a dream, who firmly believes that his linear world is the entirety of the universe. He is skeptical and dismissive of ideas that challenge his worldview.

Chromatistes is a historical figure in Flatland known for instigating the Colour Revolt by introducing painting. His actions led to a significant movement for equal rights, influencing Flatland's society.