The King Worm is a giant worm-like creature that appears as the first boss of Metroid: Zero Mission. This large rock-dwelling beast continuously bores through the subterranean depths of Brinstar, following Samus Aran and hindering her progress.
The King Worm is called a worm, though it more closely resembles a centipede. It has a long, segmented body covered in impenetrable armour plates with each segment being adorned with sharp barbs. The head of the beast sports a pair of large, spiky mandibles, between which rests a single huge eye. The eye is the King Worm's sole weak spot and attacks to any other part of the body will have no effect.
Samus can encounter the King Worm several times over the course of Zero Mission. Whenever passing through Brinstar, it is highly probable that she will be trapped by the creature and forced to fight it. It is possible to defeat the King Worm on the first encounter, however.
When Samus encounters the King Worm, it will prevent her from progressing by blocking off the passageway in front and behind her with its long, indestructible body. It will then attack the trapped Samus by burrowing out from the ceiling and attempting to snap her up in its mandibles. Also, the King Worm can shed the barbs on its body segments which will damage Samus if they touch her.
The King Worm's only weak point is its eye which can be damaged with missiles. It takes three missiles to kill the creature, although aiming can be difficult as the King Worm will use its mandibles to shield its eye.