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 Accuser Ronan the Accuser investigates the signal and battles the Fantastic Four soon after).
The Sentry is then transported by the U.S. Army to Cape Canaveral, where it is reactivated by the Kree Colonel Yon-Rogg, the leader of the Kree expedition now investigating Earth. Yon-Rogg hopes the Sentry will kill the hero Captain Marvel, another member of expedition. Mar-Vell, however, manages to defeat it.
Ronan the Accuser later reactivates the Sentry and uses it in an attempt to reverse the course of evolution on Earth, but it is once again defeated by Mar-Vell. The Kree agents attempt to retrieve the Sentry but are driven off by spy agency S.H.I.E.L.D.. The Sentry is seen again when activated by the Super-Adaptoid, who uses the robot as part of his team Heavy Metal in a bid to try and destroy the superhero team the Avengers. It was later destroyed in the series Blackwulf.
Other Kree Sentries
Sentry-9168 Another Sentry - designated 9168 - was encountered by the Fantastic Four on the Moon. Only six feet tall, this Sentry was programmed to prevent any space travellers from Earth from finding the remains of a hidden Kree city in the Blue Area of the Moon. The Fantastic Four battle and destroy the Sentry via a remote destruct mechanism.
This 30-foot tall Sentry was stationed in an unmanned supply depot/surveillance post on the planet Uranus. It was destroyed by a group of Eternals led by Uranos, sparking a war with the Kree.
This Sentry only appears once, and battles several members of the Shi'ar Imperial Guard before being damaged by the West Coast Avengers. The Sentry then self-destructs and destroys the outpost it was guarding.
Sentry 571 This version aided the Kree when their "Lunatic Legion" attacked Earth. It was defeated by the Avenger Iron Man.