I'm posting a part of Matt Williames article from his blog: Hand Drawn Nomad, (click the title to take you here). I post this portion not as criticism of Disney but as further conformation of the idea that the "Nine Old Men" and other 'stars animators' of Disney owe a tremendous amount of thanks to their assistants.
In an earlier posting called First Assistants and Clean-up: the Unsung Heroes of Animation, I published an honest and grateful acknowledgment by legendary animator Bill Tyla stating his reliance on good support from his crew.
I agree with Matt and wonder why we don't know more about these wonderful artists who helped make the Lead Animators great.
I more take issue with the "Star animator" mentality that Disney is so good at pushing. If you don't know what I mean how often do you hear about Dale Oliver? Dale was Frank Thomas' assistant for a long time, and honestly he made Frank look VERY good without getting any credit himself. Find some of Franks original ruffs, they are nothing to marvel at. Look at what Dale did with them... amazing assistant work. But you never hear about him.