Dwarves are common in the early game, and are especially easy to find in the Gnomish Mines; randomly generated dwarves are always peaceful towards dwarven and gnomish characters, and will mostly be peaceful towards other lawful characters.
1⁄4 of dwarves will have a dwarvish iron helm and dwarvish short sword. Of these dwarves, half will receive either a dwarvish spear or axe with equal probability, and a dwarvish roundshield; the other half receives a dwarvish mattock. These dwarves have a further 1⁄3 chance of receiving a dwarvish mithril coat
Dwarves are slow, but can be well equipped. Dwarf lords and dwarf kings have two weapon attacks, which makes them quite deadly when wielding a dwarvish mattock, and they can have excellent AC from their starting armor.
Dwarves with digging tools, like the mattock or pick-axe, will use them to dig through the level.
It may be worth it for a lawful character to anger and kill dwarves for their equipment, but care should be taken, as this will anger every gnome and dwarf in your line of sight, and will lower your alignment for each one killed. Pets are able to kill peaceful dwarves with no consequences.
Dwarves using a dwarvish short sword, axe, dwarvish mattock, or dwarvish spear have better armor than dwarves using a dagger or pick-axe. This is useful knowledge if you are looking for a dwarvish iron helm or mithril-coat.
Since dwarf kings and mind flayers share the same glyph, you should use farlook to correctly identify a purple h, especially at lower dungeon levels or in the Gnomish Mines, where the random h class monster can be a mind flayer.