Disney and Lucasfilm have released a "Building BB-8" featurette online -- which is included on the "Star Wars: The Force Awakens" digital/home video release -- that provides some background on the evolution and creation of Episode VII's breakout droid.
Director J.J. Abrams said in the featurette, "R2[-D2] and [C-]3PO are such classic characters. This droid, it needs to look and feel very different, and yet needs to be in the family of what Star Wars does."
Said concept artist Christian Alzmann on designing the droid, "I always called it a snowman without a chest...From there, it was trying to give him personality and attitude by those limited parts."
Check out the "Building BB-8" featurette below:
"Star Wars: The Force Awakens" is currently available on Digital HD and Blu-ray.