Anthony Daniels is the actor who has played C-3PO, the character that has appeared in all of the Star Wars feature films, including Rogue One, as well as the animated The Clone Wars. Daniels is both the body and voice of the droid. In the film saga, C-3PO was built by Anakin Skywalker and designed as a protocol droid, boasting he is “fluent in over six million forms of communication”. C-3PO and R2-D2 are the only characters to appear in every film (R2-D2 had a cameo appearance in Star Wars: The Force Awakens).
FYI, Kenny Baker played the role of R2-D2 in six of the eight Star Wars films released theatrically to date, serving as a consultant for the R2-D2 character in Star Wars: The Force Awakens. Sadly, suffering from a lung condition for years, he passed away in August of 2016.
Answer to the Bonus Question: George Lucas started casting calls for Star Wars with the condition that no-one from any of his previous movies could audition. Since Harrison Ford had appeared in a small role in Lucas’ second movie, American Graffiti (1973), it seemed he was out of the running. As luck would have it, Harrison Ford, who had gone back to carpentry to make a living, was hired by legendary producer Fred Roos to build a door in the offices of American Zoeotrope – where Lucas was holding casting calls. According to Roos, he secretly sought to have Ford there to ‘accidentally’ encounter Lucas. Which he did! Since he was there anyway, Lucas asked him to read lines for others who were auditioning – and as it turns out, did it better than anyone else.
Perhaps the amazing Harrison Ford just needed someone to open a door – the rest, as they say, is history.