Hobgoblins are frequently found in throne rooms. They will be generated with an orcish helm 50% of the time, and they also have a 50% chance of receiving a weapon (either an scimitar or an orcish dagger with equal chance). 
Hobgoblins are relatively weak and slow, and thus usually not a significant threat. As orcish monsters, they are especially useful as sacrifice fodder for orc characters to convert altars with, especially if a throne room occurs on the same floor.
The hobgoblin was originally a helpful spirit of the hearth in folklore once considered helpful, but the spread of Christianity gave it a reputation as a mischievous prankster.
NetHack hobgoblins are borrowed from the works of J. R. R. Tolkien, where the name is used to describe a larger kind of orc. In the preface of The Hobbit, he states that "Orc is not an English word. It occurs in one or two places but is usually translated goblin (or hobgoblin for the larger kinds)".
Hobgoblin. Used by the Puritans and in later times for
wicked goblin spirits, as in Bunyan's "Hobgoblin nor foul
friend", but its more correct use is for the friendly spirits
of the brownie type. In "A midsummer night's dream" a
fairy says to Shakespeare's Puck:
Those that Hobgoblin call you, and sweet Puck,
You do their work, and they shall have good luck:
Are you not he?
and obviously Puck would not wish to be called a hobgoblin
if that was an ill-omened word.
Hobgoblins are on the whole, good-humoured and ready to be
helpful, but fond of practical joking, and like most of the
fairies rather nasty people to annoy. Boggarts hover on the
verge of hobgoblindom. Bogles are just over the edge.
One Hob mentioned by Henderson, was Hob Headless who haunted
the road between Hurworth and Neasham, but could not cross
the little river Kent, which flowed into the Tess. He was
exorcised and laid under a large stone by the roadside for
ninety-nine years and a day. If anyone was so unwary as to
sit on that stone, he would be unable to quit it for ever.
The ninety-nine years is nearly up, so trouble may soon be
heard of on the road between Hurworth and Neasham.