Glen is first mentioned in Dead End 1-4 "Carried Away", when one of the demons threatens to report another to him. From this, it can be inferred that Glen has a high rank in the organization behind the rituals.
Aoi mentions that Glen destroyed most of the fairy rings after an incident occured with them wherein the fairy ring swallowed the whole station and a bus.
On the Facility Map obtained by the character Rune, one of the rooms is simply labeled Glen.
Glen is mentioned in Miss Knives library in several strange texts. He is addressed by name in these texts by an unknown associate. He discontinued Miss Knives' tests after they were all failures. This unknown associate was the one who asked him to.