The warrior, @, is a Valkyrie quest guardian. They are not to be confused with the valkyrie player monster, which is referred to as a warrior if generated at the appropriate level for that rank title.
All warriors are chaotic; this is likely because player Valkyries were chaotic prior to NetHack 3.1.0.
These strange creatures live mostly on the surface of the
earth, gathering together in societies of various forms, but
occasionally a stray will descend into the depths and commit
mayhem among the dungeon residents who, naturally, often
resent the intrusion of such beasts. They are capable of
using weapons and magic, and it is even rumored that the
Wizard of Yendor is a member of this species.