Grim Natwick Chuck Jones caricature
Grim Natwick and his "kid assistant" Chuck Jones at Ubbe Iwerks in 1933, graphite on 12 field animation paper by Grim Natwick.  

Stephen Worth, the art historian for ASIFA-Hollywood has written a detailed account of the impact that the artist and animator, Grim Natwick, had on the nascent animation film community.  Natwick's story is the story of animation in America and I think you'll find it a marvelously entertaining and informative read (plus there's a terrific short interview with Natwick about Ub Iwerks, where he met and worked with a young animator named Chuck Jones.)  

All of the posts on Natwick can be found here.