WARNING: The following contains spoilers for Alien #6, on sale now.
The alien species from the Alien franchise (most commonly referred to as Xenomorphs) have become one of the most defining movie monsters of the 20th and 21st centuries. Introduced as the titular extraterrestrial creature at the center of Ridley Scott's Alien and conceived of by H. R. Giger, the Xenomorphs are a nearly unstoppable force of chaos in the galaxy. The creatures can gestate in any creature, growing and evolving within them until they burst free from their bodies in horrific manner and grow to become even more fearsome.
The Xenomorphs are ruthless, clever, and without any sense of sympathy or humanity -- a truly inhuman creature from beyond the stars that sees humans as nothing more than a convenient tool to help grow their number -- but they may have an additional purpose. In Alien #6 (by Phillip Kennedy Johnson, Salvador Larroca, Guru-eFX, and VC's Clayton Cowles), a new purpose is given to the Xenomorphs that could radically alter how they're seen in the future of the franchise.
Prometheus and Alien: Coveneant revealed the origins of the creatures, tying them to the actions of the android David and the scientist Shaw and their attempts to confront the Engineers. David became obssessed with crafting a perfect creature that could outdo anything that his human designers could imagine. This creature eventually developed into the Xenomorphs that have largely defined the long-running franchise. Alien #6 suggests that they have a more universal purpose, however, as Iris Humphries reveals. Marvel's Alien has focused on the Cruz family, particuarly Gabe as he tries to save his son Danny who has been infected by a Facehugger. Alongside the Bishop of the station and Danny's girlfriend Iris, Gabe attempts to save his son and kill the alien inside him.
But Iris is revealed to be a freely liberated synthetic, a robot who has designs for the end of humanity -- and doing so requires the Xenomorph within Danny. After being fatally damaged following her betrayal, Iris explains her plan was to unleash the Xenomorph growing in Danny on Earth, allowing it to wipe out all organic life which would subsequently allow the synthetics to remake the world in their image. Iris reveals that she knows about the "Woman in the Dark," a vision of a humanoid Xenomorph that appeared to Gabe. Iris explains that now, when organic species "grow arrogant" enough to escape their worlds and venture into space, the Xenomorphs are waiting for them as "Prometheus' cleansing fire."
To Iris and her allies, the Xenomorphs are effectively a galactic security system, wiping out the smaller races whenever they grow too strong or ambitious. The Woman in the Dark represents the end of the world, when the alien race has wiped out all of humanity. Iris dies, telling Gabe to remember that it was his actions that brought the Xenomorphs to the Weyland-Yutani Corporation, and that it will ultimately be his fault when humanity is wiped out as a result. It's an interesting interpretation of the history of the aliens and what their actual role in the universe is, especially in light of David having been the one to have constructed the Xenomorphs in the movie continuity.
In many ways, this theory makes sense. The perfect killers, the Xenomorphs serving as the informal way the universe deals with exploring races is an interesting idea. Regardless of the technology or capability they encounter, any organic life that comes across them is doomed to a brutal end.