A kobold warrior, k, is a type of monster that appears in SLASH'EM, SlashTHEM and Hack'EM. It is the strongest non-unique kobold of those introduced in SLASH'EM, and has a weapon attack with a hit die twice as strong as a kobold lord.
As with rock kobolds, kobold warriors are distinctly more dangerous than kobolds in vanilla NetHack. Their HD of 7 lets them take a few hits, and their weapon attack is twice as damaging as that of a kobold lord. Low-level or fragile characters will want to be cautious when they first appear, and all characters should be mindful of them when they appear in large groups with their brethren, such as on the kobold level.
Kobolds are creatures that appear in many fantasy-themed works and media, which often borrow significantly from Germanic folklore - Germanic kobolds are a form of sprite that are generally benevolent if treated with kindness, but will respond to disrespect with anything ranging from pranks to even outright attacking and killing offenders.
Dungeons & Dragons in particular - and by extension, NetHack and many of its variants - depicts the kobold as a race of small reptilian humanoids with long tails, distantly related to dragons; earlier editions gave kobolds more dog-like features, which lead to many depictions of kobolds in Japanese media leaning harder in that direction after the popularity of the anime franchise Record of Lodoss War. Fantasy kobolds are often considered weak "cannon fodder" monsters that can be cunning and strong in groups, similar to goblins.
The race of kobolds are reputed to be an artificial creation
of a master wizard (demi-god?). They are about 3' tall with
a vaguely dog-like face. They bear a violent dislike of the
Elven race, and will go out of their way to cause trouble
for Elves at any time.