Nobody digging at Otricoli in 1775 was looking for the face of Zeus. Pope Pius VI had financed an excavation of a Roman town, and what came up out of the ground was a colossal marble head and shoulders, broken from whatever full length statue it once belonged to. It went straight into the new Pio-Clementino Museum the Pope was assembling at the Vatican, and it has not left the Sala Rotonda since.
What makes the bust worth pausing over is less the object itself than what it stands in for. No original statue by Pheidias, the sculptor whose fifth century BCE seated Zeus at Olympia was one of the Seven Wonders of the Ancient World, survives anywhere. Every idea anyone has of what that lost masterpiece looked like comes filtered through later copies, descriptions and echoes, and the Otricoli head, a Roman era rendering of a fourth century BCE Greek original, is one of the clearest surviving links in that chain. The deeply set brow, the slightly parted lips, the sense of contained authority rather than active gesture: these are read by scholars as inherited traits, carried down through generations of copying from an image nobody alive has ever actually seen.
That secondhand status did nothing to limit its influence. From the moment it went on display, plaster casts and engravings of the Otricoli Zeus spread across European academies and art collections, and it became, by sheer repetition, one of the most familiar faces of Zeus in Western art, arguably more widely reproduced than any statue of him that has survived complete.