The Destroyer was a large Alien that was encountered by Alecto Throop and her team during their expedition into the ruins of an ancient city that had belonged to the long, extinct Space Jockeys. It was created when one of Throop's androids (corrupted by a Weyland-Yutani command overwrite) infected a surviving Space Jockey with a Facehugger, thus the Destroyer was born.
Like the human-spawned Aliens, the Destroyer and it's kind have a skeletal, biomechanical appearance. They also have a few set of dorsal tubes and a flat ridge of spines located on their backs. They have a large body size and great physical strength, having been shown to be capable of leveling the ancient city and crushing its human-spawned brethren with little effort. Instead of having segmented tails, the Destroyers have a ridged tail with a set of tubes on each ridge, though they still have the blade at the tip of the tail.
Like other Aliens, the Destroyer have elongated, cylindrical skulls with no visible eyes and possess "inner jaws." It also incorporated several traits taken from the Space Jockey, such as brown-clad armor and possessing the trunk located in the middle of the mouth coming from the nasal area to the chin area, though the trunk is not attached and becomes separated when the Destroyer opens its mouth.
According to Dr. Lucien Keitel, the Aliens first appeared one and one-half billion years ago to exterminate the Space Jockeys as they have become the most dominant race in the galaxy at the time. Using the Space Jockeys as hosts, Aliens of the same kind as the Destroyer were born and eventually succeeded in exterminating the Space Jockeys, therefore restoring balance in the galaxy.
In 2142, deep-space rescue specialist, Alecto Throop, was sent at the request of the Geholgod Institute to locate Dr. Keitel. Their search led Throop and her team to the Space Jockey's ancient city. One of Throop's synthetics, Baal, became infected with Weyland-Yutani's subversion programming and under the programming's influence planted an egg near the last living Space Jockey. A facehugger emerged from the egg and attaches itself to the Space Jockey that was barely living, creating the Destroyer. The Destroyer crushed Baal and began to wreak havoc in the ancient city, killing its own human-spawned brethren and causing the ancient city to cave in. The Destroyer later makes its last appearance as an unlikely hero. When Alecto and her remaining crew are escaping the ancient city aboard the Rachel, am Alien snuck aboard the ship. As the Alien prepares to attack, the Destroyer grabbed it through the bay, allowing Alecto and her crew to escape.