Stalker
The hunter carrying vengeance for the night of the Naga Drums, fleeing the resemblance between the Tenno and himself.
Hunhow's weapon
In The Second Dream he joined with Hunhow, took the Shadow Stalker form and received the War blade. Reaching the Reservoir, he hesitated at the sight of the Operator's child body. It is implied he may share an origin with the Tenno, but his full past is never confirmed.
The Acolytes
The Acolytes around him carry his hatred of the Tenno alongside grievances of their own. Their bonds rest less on a classic faction hierarchy than on a shared doctrine of vengeance.
The mystery of his identity
Whether the Stalker is an independent Warframe, a forgetful Tenno using Transference, or some other transformation entirely has never been fully verified. A trustworthy file preserves that uncertainty instead of mixing the explicit scenes with theory.