Argus Panoptes
In the version of the story in which Zeus transformed Io, the deception failed, and Hera begged Zeus to give her the heifer as a present, which, having no reason to refuse, he did. Hera then sent Argus Panoptes, a giant who had 100 eyes, to watch Io and prevent Zeus from visiting her, and so Zeus sent Hermes to distract and eventually slay Argus. According to Ovid, he did so by first lulling him to sleep by playing the panpipes and telling stories. Zeus freed Io, still in the form of a heifer. In some myths, Hera uses Argus' eyes to decorate her peacock's feathers to thank the giant for his help.