Jacques Copeau, a seminal figure in 20th century theatre theory and practice, developed a distinctively Aristotelian approach to actor training, focused on sincerity and embodiment. Earlier scholarship has misrepresented Copeau's theatre practice and aesthetics as essentially Nietzschean, overlooking the deep influence on his work of the educational philosophy of Maria Montessori. Previously unexplored archival evidence shows Copeau had an active professional relationship with Montessori, and he incorporated her child-centered Aristotelian philosophical anthropology into his own physical approach to acting and his aesthetics of poetic realism. The epistemology and metaphysics of the human body that animate both Copeau's theatre and Montessori's auto-education were influenced by the Thomist aesthetic theory of Jacques Maritain. Montessori's practical and philosophical framework clarifies the coherence of Copeau's selective synthesis of contemporary theories of theatre, mask and music, including those of Andr? Antoine, Edward Gordon Craig, Adolphe Appia and ?mile Jaques-Dalcroze. Copeau's Montessorian child-centered perspective, with its important metaphysical presuppositions and ethical ramifications for the actor's process and the role of theatre, has a continuing influence in theatre theory and practice. Michel Saint- Denis, Copeau's nephew, brought Copeau's actor training and theoretical approaches to England, Canada and the U.S.A., and strove to implement these faithfully without using the language of their philosophical substratum. In contrast, Jean Dast?, Copeau's son-in- law, keeping Copeau's child-centered philosophy and its semantics, contributed to the movement to decentralize theatre in France, and influenced the currently prestigious acting school of Jacques Lecoq. Copeau's ideal of the actor's sincerity, closely linked to his use of the mask in actor training, has also been pivotal in recent theory and practice. L?on Chancerel popularized Copeau's vision through the Scouts of France and its professional company, Les Com?diens Routiers and influenced the contemporary theatre company - the Th??tre de l'Arc en Ciel - through its founder, Olivier Fenoy. Through Chancerel, the Vieux Colombier's signature theatrical element, the "noble" mask (more often in current scholarship and practice referred to as the "neutral" mask), became the progenitor of the "visage neutre" of Fenoy's company and its educational arm the Acad?mie de Th??tre pour Enfants in France. These latter disciples also inherited Copeau's Montessorian perspective on the actor's process incorporating the original idea behind training with the "neutral mask" and learning to attain a "child-like state." They thus continue Copeau's vision of theatre true to Aristotelian embodiment, an embodiment of fictive character that demands in the first place a Montessorian education of the actor as a unique fusion of embodied soul and a "dependent rational animal."