This is a dog. Demon dog.
They resemble regular dogs from Wolfenstein 3D, but have been possessed by Triad demons, turning them into bloodthirsty beasts.
In the description of the original RotT specification there are two versions of dogs:
1 - "Dogs - same"
2 - "Demon dogs - Add red eyes, make 'em twice as fast, twice as much damage, twice as many hit points."
Of course, I chose option number 2. Demonic beasts in the service of the Triad. I thought that creating a second dog didn't really make sense.
credit: Apogee
FB Rise of the Triad: Wolfenstein 3D Part II - FB Site
