The monster known for its many eyes in Greek mythology is Argus, also referred to as Argus Panoptes. He was tasked with guarding Io, a lover of Zeus, and was notable for having a hundred eyes, making him a formidable watchman. Argus was eventually killed by Hermes, who was sent by Zeus to free Io. His eyes were said to be transferred to the tail of the peacock, which later became associated with the goddess Hera, symbolizing vigilance and protection.