The First One is a clayborn modeled from The Sculptor. It's the first creation of his, and appears to be a mindless automata with no will of it's own. Throughout the course of Grey Irma's interactions with it, subtle impressions are left of a deeper understanding.
The First One is the first phase of The Sculptor boss fight. Rather than attacking directly, it repairs broken Dark Mirrors The Sculptor can use to summon enemies. After falling in battle, The First One apologizes to Grey Irma which is the first time it speaks.