“At first, C-3PO was not intended to be a robot but a Morphlak, a humanoid species that were only of male gender, but the studio wasn’t too open about the idea of a gay character, let alone a whole planet sustaining a gay species” he remembers. “You have to remember it was the 70′s, people were far more uncomfortable about the topic of LGBT rights at the time. It made the producers, lets just say, pretty uneasy, so we eventually changed his character to an asexual robot”

Basically he was the gay member of the group, who was continuously annoying the other characters, and whom they felt comfortable ignoring the advice of. His only redeeming quality was that he could translate R2D2 for Han, Leia, and Chewie (and thus for us). The trope for him is butt monkey, right? And he's gay/effeminate because... gay people were acceptable targets in 1977?

I'm just going by the movies - I have not read any of the books or watched the cartoons - maybe something happens in them that redeems the character / characterization.