It is my expert opinion that the C-3PO "persona" is created by Anakin Skywalker as a means of separating and cordoning off those aspects of his personality deemed weak, fearful, or cowardly (with the notable exception of "Yippeeee!"). By creating and then setting aside the C-3PO "persona", Anakin is able to focus - to obtain the control over his life which he so desperately desires.
While the creation of the physical C-3PO is certainly a conscious act, the psychic dissociation associated with C-3PO's creation may well have been (and probably was) an entirely subconscious/unconscious act.
Anakin is ambitious and driven to obtain the power so clearly missing from his early life as a slave. C-3PO, directionless and weak, wanders through life, being buffeted from place to place, fumbling his way through, accepting his "lot in life." In Episode IV, he commiserates with R2-D2: "We seem to be made to suffer."
It is notable that Anakin creates C-3PO originally without a skin - fully vulnerable - while simultaneously embarking on a journey which will provide the young Jedi with his own thick, protective armor.
It is further notable that soon after the creation of C-3PO, Anakin is freed from slavery and inducted into the ranks of the Jedi (merely coincidence or a reflection of Anakin's newfound focus?).
As a brooding, angry young Jedi, Anakin dons a black mantle, while C-3PO, in his innocence, eventually gains a golden skin.
C-3PO - a protocol droid - lives a life of service to others (a continuance of Anakin's childhood slave mentality) - bowing and scraping, making excuses, and lagging behind, while Anakin soars to a position within the highest echelon of the Empire.
However, as we witness in Episode VI, with all of his foibles and faults, C-3PO still manages to attain greatness. He saves the Rebel party on Endor and is recognized as a "god" by the Ewoks.
C-3PO's Ewokian godhood is rather interesting. This race of simple, (relatively) peaceful, loveable, soft creatures stands in direct contrast to Anakin's cold, metallic, ruthless Stormtrooper army. C-3PO becomes, shall we say, the "king of the teddy bears", surrounding himself with all that is childlike, meek, and innocent.
Anakin, striving blindly forward, eventually recognizes his folly and is cleansed as he perishes within the Emperor's cold blue fire. It is said that Anakin's final, nearly-inaudible whisper was "three-pio"...