It is the first miniboss that Samus fights in Zero Mission. The King Worm is a monstrously long, multi-segmented worm with a single eyeball and no other visible orifice or appendage. Its powerful, bony pedipalps and spikes that protrude from its body allow it to easily tunnel through solid rock. It stalks Samus as she traverses the introductory caverns of Brinstar, and makes its appearance after you collect a Missile Upgrade. When it is defeated, the Charge Beam appears.
The King Worm can be fought multiple times, as it runs away if you don't kill quickly enough. After it blocks you in, the King Worm's head will appear at the top-middle of the screen. When it opens its eye, immediately shoot it with a Missile. It will then move straight downward, so move to the left or right of it to avoid getting hit. Three hits with a Missile will kill it. Beware touching its spiky body on either side of the screen, but be sure to shoot the spikes that fall off it for extra Health and Missile ammo.
Its Japanese name is Deiorumu (デイオルム) pronounced "Day-oh-roo-moo". "Deo" means "God" in Latin, and the Japanese word for "Great King" is "Daioh" (大王) so the first half of the name could possibly be a combination of the two. "Rumu" is a romanization of "worm".