The hezrou, &, is a demon in NetHack. They are slow, but can hit hard. Like any non-balrog, non-foocubus major demon, polymorphing into a hezrou and attacking a monster with bare or gloved hands grants a 1/13 chance per hit landed to summon tame demons with the message "Some hell-p has arrived!"
Polymorphing into a hezrou is not very useful; they are very slow and large. You will break your shirt, cloak and any body armor. If this happens to you unintentionally, perhaps as the result of a polymorph trap, try attacking bare-handedly to summon some pet hezrou.
A pet hezrou will not summon more demon monsters - tame or otherwise - when they fight.
"Hezrou" is the common name for the type II demon. It is
among the weaker of demons, but still quite formidable.