# W. Ross Ashby > [[PORTAL_Systems_science|Systems science]] · [[PORTAL_Decision_theory|Decision theory]] spine. ## Microsim — queued <p class="wt-pending"><strong>Microsim in the draft queue.</strong> No dedicated interactive station exists for this biography; the sourced overview below is complete and citable now.</p> William Ross Ashby (1903–1972) was an English psychiatrist and one of the founding theorists of cybernetics, described by contemporaries as the field's major systematiser after Norbert Wiener. His two books, Design for a Brain (1952) and An Introduction to Cybernetics (1956), brought rigorous, general mathematical treatment to ideas about self-regulation and adaptive behaviour that had previously been described only informally. ## Overview Ashby's best-known contribution is the law of requisite variety: a regulating system can only control a process to the extent that the regulator has at least as much variety — as many distinct possible states or responses — as the disturbances it must counteract. He also built the homeostat, an electromechanical device that demonstrated self-regulating, adaptive behaviour by automatically reconfiguring itself to return to stable equilibrium after being disturbed, one of the earliest physical demonstrations of what would later be called a self-organising [[Complex_system|complex system]]. His work sits at the root of [[Systems_science|systems science]], [[Cybernetics|cybernetics]], and [[Decision_theory|decision theory]]'s treatment of regulation and control under uncertainty, and continues to be cited directly in complex-systems and [[Systems_theory|systems-theory]] research today. **On the spine:** [[Systems_science]] · [[Decision_theory]] · [[Cybernetics]] · [[Complex_system]] · [[Systems_theory]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/W._Ross_Ashby) : [Wikitube](https://en.wikitube.io/wiki/W._Ross_Ashby) --- *Repopulated 2026-08-05 · Wikipedia-sourced overview · 0 deletions.*