Half-Life Alyx: 13 Biggest Questions Answered For New Fans
9. What Is Xen?
Since we keep bringing Xen up, let’s break it down.
Xen, or Border World, is the planet in which the Black Mesa Incident caused Earth to link with via portals. The Combine are not from Xen, they were simply knowledgeable of it when tracking down the Nihilanth.
The Nihilanth is a giant telepathic alien baby, basically, who is failing in a war against the Combine. He’s also not a nice guy, enslaving the Vortigaunts and using them to fight for him - against the humans at Black Mesa, for example. Many alien enemies we know, such as the aforementioned headcrab, vortigaunt, barnacle, etc. are all from Xen.
Gordon was teleported here to close the inter-dimensional portal controlled by the Nihilanth, and did so, killing it and freeing the vortigaunts. This is why the vortigaunts have a huge crush on the Freeman in Half-Life 2. They’re super thankful.
After Gordon finishes his "work", he is transported to an unknown location to talk with the G-Man.
Gordon is congratulated and given two choices: work for the G-Man or be taken, unarmed, to a hostile area full of the species he just massacred.
Canon states you take the G-Man’s offer and are put in stasis.