Who changed bc to ad?

back in the day when BC and AD had no meaning to anyone in the surrounding area of the known world; a little known Genevieve created an illusion for his grandson of four years of age. This illusion soon caught on with the locals around the Italian city Genoa and the splitting of the old world and the beginning of the new was duly noted by the pref-ex AD and suffix of BC. The realm of authority soon decided to accept this as an adage to their somewhat bleak future and AD caught on and has since become our standard of thought.