The dwarf thief is a monster added in SLASH'EM. They are not randomly generated and will only appear in Minetown. It has a weapon attack and a theft attack; it can teleport away after a successful theft, but does not teleport randomly, and nor does its corpse convey teleportitis.
These are considerably less of a threat than the nymphs they replace in Minetown. They tend to have slightly better AC than nymphs, but are half as fast, and have only one theft attack. Their inability to teleport randomly makes them considerably easier to track down and kill if they do steal something.