Owlbear

An owlbear,, is one of the more dangerous low level monsters you'll face in NetHack, although usually not as lethal as those that appear in groups (like soldier ants). As the name suggests, they are a cross between a giant owl and a bear; standing upright on two legs with fur, feathers, and a beak.

Owlbears have bearhug attack that holds you in place and crushes you. They were introduced way back in Hack 1.0 and were probably inspired by the Dungeons & Dragons monster of the same name.

Strategy
You can safely kill an owlbear from afar with ranged weapons, spells, or wands. If you are caught in the bearhug attack, you can teleport away. Using sleep or paralysis, such as from a wand of sleep or thrown potion, on the owlbear has a chance of releasing you, but not always (and if not, it also might wake the owlbear when you try to move away).