This is a really thorough history of the development of Chewie.
The most interesting aspect of the piece is that Lucas very likely stole the look of Chewie from a science fiction illustration by John Schoenherr. The side-by-side comparison of the drawings is pretty damning -- practically infringement territory.
The major difference, however, is the Schoenherr creatures had six breasts which Lucas and Ralph McQuarrie opted not to borrow.