The umber hulk is a monster in NetHack. It is one of the few monsters which can tunnel naturally through rock (along with rock moles and woodchucks) and unique through its confusion gaze attack. Wearing a blindfold while fighting protects against this but not its other attacks.
Umber hulks are the only member of the U Umber hulk monster class.
Apply a mirror to one and it will automatically confuse itself. Useless, but fitting.
Because umber hulks are stronger, faster, and do not eat metal like rock moles, they make excellent pets for their ability to tunnel. By using a magic whistle, one could easily tunnel through large maze levels (such as Gehennom) without requiring power to cast the spell of dig, using charges from a wand of digging, or carrying around a heavy pick-axe or dwarvish mattock.
Hostile umber hulks can also be useful for tunnelling purposes; simply try to avoid killing them unnecessarily.
Umber hulks are powerful subterranean predators whose
iron-like claws allow them to burrow through solid stone in
search of prey. They are tremendously strong; muscles bulge
beneath their thick, scaly hides and their powerful arms and
legs all end in great claws.