1. Argus ("bright") (also known as Panoptes) is a monster with a hundred eyes. He was thus a very effective watchdog, as only a few of the eyes would sleep at a time; there were always several eyes still awake. Argus was Hera's servant; her last task for him was to guard a white heifer from Hera's husband, Zeus. Hera knew that the heifer was in reality Io, one of Zeus' many girlfriends.
To free Io, Zeus had Argus slain by Hermes. Hermes succeeded in putting all of Argus' eyes asleep with boring stories, being disguised as a shepherd. To reward good service, Hera had the hundred eyes of Argus preserved forever, in a peacock's tail.
Ovid I, 625.
2. Argus (or Argos) is also the name of a long-lived dog owned by Odysseus in Odyssey. When Odysseus returns from his voyages and wears the disguise of a beggar that Athena places upon him, only Odysseus's old dog, Argus, recognizes him.
3. Argus in the tale of the Argonauts is a shipwright, the builder of the ship the Argo, named after its builder. The vessel was used by Jason in his quest for the Golden Fleece, Jason and his compatriots called themselves Argonauts, after the ship.