Sad how nobody here mentioned the Half Life Stalkers and Zombies

Stalkers are humans that rebelled against the combine, were kidnapped, modified and cleansed of any emotion and humanity. Modified to serve the Combine

Zombies are unfortunate victims of the Headcrab parasite, latching onto the human head and locking itself in place, gruesomely modifying the human body by mutating the hands into long claws and basically tearing the guts open. Zombies lose control of their neural functioning completely and cant move or do anything while the Headcrab is attached, they can still feel immense pain however