Argus is a noun that refers to a watchful guardian.
In Greek mythology, Argos was a giant with many eyes. As time went by, it was often said that a watchful person had ‘the eyes of Argos.’ The name itself later became a reference to a guardian, as in: Tyler served as an argus while we trekked further into the woods. He kept a watchful eye, making sure we didn’t get any surprises from things like bears.