In Welsh mythology, Modron ("divine mother") was a daughter of Avalloc, derived from the Gaul goddess Dea Matrona. She may have been the prototype of Morgan le Fay from Arthurian legend. She was the mother of Mabon.

In the Dungeons & Dragons fantasy role-playing game, modrons are a monster native to Mechanus, the Outer plane of law. Modrons are living creatures that resemble geometric shapes with humanoid limbs. In later (post-Gary Gygax) versions of Dungeons & Dragons, the Plane of Law was renamed from Nirvana to Mechanus and the Modrons were changed into clockwork robot-like creatures called Inevitables. Modrons have a strict heirarchy, with each rank reporting to the rank directly above it, and issuing commands to the ones ranking directly beneath it. For example, a Quadrone modron will report to a Pentadrone, and command several Tridrones. But it will not recognize Duodrones or Monodrones as being of the Modron race. In the Planescape campaign setting, one can play as a Rogue Modron, a modron who has left Mechanus and broken his link to the other Modrons.