Argus Panoptes

[1] Probably Mycene[2] (in another version the son of Gaia[3]) was a primordial giant whose epithet Panoptes, "all-seeing", led to his being described with multiple, often one hundred eyes.

His great service to the Olympian pantheon was to slay the chthonic serpent-legged monster Echidna as she slept in her cave.

[7] Hera's defining task for Argus was to guard the white heifer Io from Zeus, who was attracted to her, keeping her chained to the sacred olive tree at the Argive Heraion.

The messenger of the Olympian gods, disguised as a shepherd, first put all of Argus' eyes asleep with spoken charms, then slew him.

[3] The sacrifice of Argus liberated Io and allowed her to wander the earth, although tormented by a gadfly sent by Hera, until she reached the Ionian Sea, named after her, from where she swam to Egypt and gave birth to a love child of Zeus, according to some versions of the myth.