A June 1978 screen test for the character, hosted by sound designer Ben Burtt, has surfaced and it's essentially walkthrough of the character prototype before he had ever appeared on screen. This would be six months before he made his first appearance (as superfans know) in the reviled "The Star Wars Holiday Special," and two years before "Star Wars: Episode V- The Empire Strikes Back." So it would be safe to assume that Lucas already had some idea this character was special from the start.
Anyway, it's a intriguing bit of history nonetheless. Check out the footage below and remember, we could be seeing a spinoff movie in the not too distant future, in the galaxy you already live in. [Flicksided]