The Sentries' main purpose is to stand guard over military outposts and depots throughout the Kree Empire. Sentry-459 accompanied a Kree scientific party that journeyed to Earth to experiment on sub-humans (which in turn created the race the Inhumans). When the Kree left Earth, Sentry 459 remained to monitor Inhuman progress, so that the Kree could later use them as a militia force. Sentry-459 remained inert but observing until activated by the superheroes the Fantastic Four, who fought it to a standstill. Considering itself defeated when the Fantastic Four escaped, the Sentry sent a signal to the Kree alerting them to the presence of meta-humans on Earth and then deactivated itself (the Kree Ronan the Accuser investigates the signal and battles the Fantastic Four soon after).