A great article that discusses Anthony Daniels' career and being the only actor to appear in every STAR WARS film.
That's why C3PO works. He runs close to Jar Jar, but it is naivety, not idiocy, that underlies his comedic behavior. C3PO is more than an "engine of exposition and continuity". Having C3PO in tow keeps the protagonists from becoming too cool. Somewhat like the shittiness of the Millennium Falcon, his incongruity with the narrative makes the heroes more human.
I wish Kachka would have asked about slavery. Daniels must have serious thoughts on it.