S-4QD was the only droid left on Tilnes by 31 BBY. At that time, he had been shut down by moon's electromagnetic pulses ninety-three times. Nineteen of those times his memory had been wiped, and twice his photoreceptors had popped out of his head. He could no longer say quite what his purpose on Tilnes was, and wasn't that sure that S-4QD was actually his name.
S-4QD was a protocol droid that had been sent to Tilnes as a representative for the droids of Uffel. They quickly realized that Tilnes had no future for droids, but left 4QD there in an advisory capacity. He ended up giving out pieces of esoteric information in conversations which served no purpose in moving that conversation along. He was a grumpy droid who always predicted that the next electromagnetic pulse would finish him off.