In Greek mythology, what was the name of the hundred-eyed watchman of Io?

In Greek mythology, the hundred-eyed watchman of Io was Argus Panoptes.

Argus Panoptes was a giant whose name means “all-seeing.” Sources commonly describe him as having one hundred eyes, with some eyes always awake. Hera appointed him to guard Io, a mortal woman whom Zeus had transformed into a white heifer to conceal their relationship.

Hermes was sent to rescue Io. He lulled Argus to sleep by playing music and telling stories, then killed him. Hera honored her faithful servant by placing his eyes on the tail of her sacred bird, the peacock.

Argus Panoptes is easy to confuse with Argos, Odysseus’ dog, and with Talos, the bronze guardian of Crete. The epithet “Panoptes” is important because it distinguishes the many-eyed giant from those other figures. Io’s wanderings later became connected with the naming of the Ionian Sea in mythological tradition.