He was an actor and the creator of an important school of acting...
It is not easy to say what is "essential". (For myself? for everybody? for today or in all times etc.) What is essential depends by a context which does it essential or not, and all contexts are not similar...I always combine ideas that I find in different sources..In any way as you suggest "They are not necessary to deal with animation directly" I can mention books that I like and are references for me.
- Rudolf Arnheim, Art and Visual Perception, A Psychology of the Creative Eye, University of California Press, 2004
- Jacques Lecoq, Le Corps poétique : un enseignement de la création théâtrale, Actes Sud, 1999
- Various Books on Bauhaus
- Betty Edwards, Dessiner grâce au cerveau droit, Mardaga, 2014
- Giannalberto Bendazzi, Pages d'Alexeïeff, Annecy,14e JICA, 1983
- Giannalberto Bendazzi, Animation: A World History, Focal Press, 2015
- Theodor Adorno, Aesthetic Theory, University of Minnesota Press, 1998