Who was responsible for decorating the peacock's tail?

The correct answer is Argus. In mythology, Argus Panoptes was a giant with many eyes who served Hera, the queen of the gods. Argus was tasked with watching over Io, a priestess of Hera who had been transformed into a cow. To reward Argus for his vigilance, Hera later transformed his eyes into the feathers of the peacock, which is often associated with her as a symbol of beauty and fidelity. This transformation explains the distinctive eye patterns found in a peacock's tail, connecting Argus directly to this decorative aspect.

The other figures listed have notable roles in mythology, but they do not have this specific association with the peacock. Zeus, for example, is known for his many exploits and children, but he did not play a role in decorating the peacock’s tail. Hercules is famous for his twelve labors and heroic feats, but he is not connected to the peacock. Lastly, although Panoptes refers to the "all-seeing" nature of Argus, it is not the proper name of the giant responsible for the peacock's tail decoration. Thus, Argus is the figure who is recognized for this specific mythological detail.