Video Transcription
And according to the art book, it was an individual that wasn't compatible with Ruvik, but completely succumbs to STEM and completely lost his identity.
Going rabid, Heresy went on a rampage, consuming all the consciousness he could find until he eventually transformed into this.
Oh yeah, and the art book says that that pipe in his mouth feeds him his own shit to sustain him, so that's nice.
Nice bit of lore, I love lore.
Anyway, this chapter is extremely short, but it reeks of Resident Evil.