Controller 4

Controller 4 is The Mouth or Teeth.

Controller 4 was the assistant on Project Kiteboy and the Lead on Project Che Guevara.

Relations to the Story
He cut off Controller 1's hand in order to activate Controller 2 to do some "work with the void". In the video "reset" he got stabbed and then burned by Controller 1.

Character Traits
Appearance: Humanoid wearing black hoodie with skull mask

Speculation and Theory
Controller 4 may be the brother of Controller 1.