The iron golem is one of the tougher golems. Their breath is poisonous and can drain your strength. On creation, they have a chance of a battle axe or a two-handed sword or a bow and 3-14 arrows or a longsword or a lucern hammer or (64% chance) nothing. They are not eligible for a random offensive item.
When killed, an iron golem's corpse will be some number of the infamous iron chains, widely considered one of the most useless items in NetHack--although some players do find the occasional odd job for one, such as keeping an Elbereth activated or marking the Vibrating square. As iron chains are quite rare, it is worth consulting that entry when you dispatch an iron golem.