Modilus was a giant red color Mechanical Monster, built in the image of a Bull, which was only featured on Ep.14 of the original Mazinger Z Anime, fighting Spartan K5 on an exercise training. He had 5 horns, small thorns on the side of its snout and could fire missiles from it's mouth. Modilus was one of a few Mechanical Monsters to not feature an Code or Number designation at the end of its name, and may have been a Monster meant for training other Mechanical Monsters rather than war.

During the exercise, Modilus fought Spartan and tried to take him down when the beast failed to go on the offensive, but was beaten, presumably damaging it, as Modilus was never featured again.