Residing in a galaxy far, far away, C-3PO is a protocol droid who is not very good at telling stories, well at least ones that are very interesting anyway. Originally built by Anakin Skywalker to aid his enslaved mother, C-3PO was designed to understand human behavior as well as to be a universal interpreter for both droids and living species.
His face was designed to be as neutral as possible so that he could display any type of emotion through use of body language and voice; therefore relieving the need for complex facial mechanics. Throughout his life, he would go through many hardware changes, as well as memory erasures. He started off as a naked droid in development, then he was covered in drab tin, and then finally he was outfitted with a golden colored alloy so as to improve his bling bling factor.
And as any interpreter should be, he was programmed to be very conciliatory to humans, droids, and other intergalactic life forms. Sometimes, however, this becomes an annoyance to his neighbors. That is why he has a shutoff switch behind his neck.