The wumpus, q, is a very slow but strong monster in NetHack.
The wumpus can cling to ceilings, allowing it to be generated over and move through water without drowning or being relocated. You can ride a pet wumpus while on land, but if you try to ride over water, you will fall off the wumpus and into the water, wetting your inventory and possibly drowning. If you don't drown, you end on an attached land square, and the wumpus will be on the water square you tried to ride on; the saddle stays on the wumpus.
It is a rather rare creature but not among the rarest. Should you ascend a game, you are pretty much guaranteed to meet at least a few wumpuses.
Wumpuses generated as part of a level usually start off asleep (80% chance), though this does not apply to any wumpuses generated after level creation, or any wumpus generated after you have picked up the Amulet of Yendor.
The Ranger quest locate level has a guaranteed wumpus.
The Wumpus, by the way, is not bothered by the hazards since
he has sucker feet and is too big for a bat to lift. If you
try to shoot him and miss, there's also a chance that he'll
up and move himself into another cave, though by nature the
Wumpus is a sedentary creature.