Geometric Knight is a series of three anime-only monsters used by Clark Smith in the Yu-Gi-Oh! 5D's anime, all of which are based on geometric shapes.

The three monsters are "Triangle Knight", "Hexa Knight" and "Decago Knight", based on a triangle, hexagon and decagon respectively. A recurring theme of these monsters is that their Levels are equal to the number of sides on their corresponding shapes; "Triangle" being Level 3, "Hexa" being Level 6, and "Decago" being Level 10. The corresponding shape is visible in the background of their artwork, and their shields are shaped in the corresponding shape.

Their effects also seem to be tailored for Concentration Duels, as they can be easily abused in them as shown by Clark.