C-3PO was a protocol droid with an identity crisis and no crisis management programming. Fortunately for him he had a best friend that looked out for him.
The Early Years
C-3PO was built by Anakin Skywalker when Skywalker was just a little boy. Anakin was a slave and unable to provide the coverings which lead to more than one embarrassing moment for 3PO. Yet another embarrassing facit of C-3PO's excistance was that Anakin programed his language center with a sales idiom base, based on a used ship salesman from Corellia, and the speech patterns of a fashion designer from Coruscant. Right before Anakin left to become a Jedi C-3PO was introduced to R2-D2 whom he finally felt was a droid he could connect with. R2 did not feel the same but kept his mouth shut because he was good at that sort of thing. After Anakin left 3-PO was acquired by Cliegg Lars when he bought Shmi Skywalker. C-3PO then spent most of his time looking after Owen Lars and when he was old enough procuring illcit videos and pictures for the boy to lock himself in his room with.
The Clone WarsC-3PO was re-united with his maker Anakin Skywalker when Shmi Skywalker was taken by Tusken Raiders. When Anakin was allowed to take the droid nothing made him happier. More and more he was being required to stay in the closet when Beru was over and C-3PO was uncomfortable with the recordings in his memory banks. During the rest of the Clone Wars he spent his time being useless and trading gossip about Anakin and Pade with R2-D2. Towards the end he did help R2 drag Pade back in the ship after Anakin went Ike Turner on her but his clumsiness may have caused her ultimate demise. After that his memory was wiped.
The RebellionThe next twenty years of 3PO's life were spent in the service of Alderaan's royal family. They were nice. Then on a routine flight with the princess C-3PO and R2-D2 had to escape and ended up on Tatooine. In an amazing coincidence, considering the size of the galaxy and number of sentient beings in it, they were bought by Owen Lars who did not seem to reconise either of them. Later they ran into Obi-Wan Kenobi who also knew the both of them for years and acted like he did not. This cause great confusion for 3PO since he didn't remember them either(memory wipe) but R2 spent much of the first day with the two of them muttering about stupid ungrateful humans. Once again in a time of war C-3PO spent much of his time being useless, slowing the heros down, and bragging about his knowledge of 6 million forms of communication. What happened to him after the rebellion no one really knows because no one really cares.
While C-3PO frequently bragged about how many "forms of communication," he knew, most of them were actually offensive hand gestures, and internet memes.